< draft-ietf-drums-msg-fmt   rfc2822.txt 
Network Working Group P. Resnick, Editor
INTERNET-DRAFT QUALCOMM Incorporated
<draft-ietf-drums-msg-fmt-08.txt> January 26, 2000
Internet Message Format
Status of this memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task Network Working Group P. Resnick, Editor
Force (IETF), its areas, and its working groups. Note that other groups Request for Comments: 2822 QUALCOMM Incorporated
may also distribute working documents as Internet-Drafts. Obsoletes: 822 April 2001
Category: Standards Track
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at Internet Message Format
http://www.ietf.org/shadow.html.
Note: Though this document uses the word "standard" in both the title Status of this Memo
and the body of the text, it is of course still an Internet Draft and is
NOT actually a standard until it has been approved and published as an
RFC.
This document expires July 26, 2000. This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved. See Copyright (C) The Internet Society (2001). All Rights Reserved.
Appendix C for further information.
Abstract Abstract
This standard specifies a syntax for text messages that are sent between This standard specifies a syntax for text messages that are sent
computer users, within the framework of "electronic mail" messages. This between computer users, within the framework of "electronic mail"
standard supersedes the one specified in Request For Comments 822, messages. This standard supersedes the one specified in Request For
"Standard for the Format of ARPA Internet Text Messages" [RFC-822], Comments (RFC) 822, "Standard for the Format of ARPA Internet Text
updating it to reflect current practice and incorporating incremental Messages", updating it to reflect current practice and incorporating
changes that were specified in other RFCs [STD-3]. incremental changes that were specified in other RFCs.
Table of contents Table of Contents
[TBD] 1. Introduction ............................................... 3
1.1. Scope .................................................... 3
1.2. Notational conventions ................................... 4
1.2.1. Requirements notation .................................. 4
1.2.2. Syntactic notation ..................................... 4
1.3. Structure of this document ............................... 4
2. Lexical Analysis of Messages ............................... 5
2.1. General Description ...................................... 5
2.1.1. Line Length Limits ..................................... 6
2.2. Header Fields ............................................ 7
2.2.1. Unstructured Header Field Bodies ....................... 7
2.2.2. Structured Header Field Bodies ......................... 7
2.2.3. Long Header Fields ..................................... 7
2.3. Body ..................................................... 8
3. Syntax ..................................................... 9
3.1. Introduction ............................................. 9
3.2. Lexical Tokens ........................................... 9
3.2.1. Primitive Tokens ....................................... 9
3.2.2. Quoted characters ......................................10
3.2.3. Folding white space and comments .......................11
3.2.4. Atom ...................................................12
3.2.5. Quoted strings .........................................13
3.2.6. Miscellaneous tokens ...................................13
3.3. Date and Time Specification ..............................14
3.4. Address Specification ....................................15
3.4.1. Addr-spec specification ................................16
3.5 Overall message syntax ....................................17
3.6. Field definitions ........................................18
3.6.1. The origination date field .............................20
3.6.2. Originator fields ......................................21
3.6.3. Destination address fields .............................22
3.6.4. Identification fields ..................................23
3.6.5. Informational fields ...................................26
3.6.6. Resent fields ..........................................26
3.6.7. Trace fields ...........................................28
3.6.8. Optional fields ........................................29
4. Obsolete Syntax ............................................29
4.1. Miscellaneous obsolete tokens ............................30
4.2. Obsolete folding white space .............................31
4.3. Obsolete Date and Time ...................................31
4.4. Obsolete Addressing ......................................33
4.5. Obsolete header fields ...................................33
4.5.1. Obsolete origination date field ........................34
4.5.2. Obsolete originator fields .............................34
4.5.3. Obsolete destination address fields ....................34
4.5.4. Obsolete identification fields .........................35
4.5.5. Obsolete informational fields ..........................35
4.5.6. Obsolete resent fields .................................35
4.5.7. Obsolete trace fields ..................................36
4.5.8. Obsolete optional fields ...............................36
5. Security Considerations ....................................36
6. Bibliography ...............................................37
7. Editor's Address ...........................................38
8. Acknowledgements ...........................................39
Appendix A. Example messages ..................................41
A.1. Addressing examples ......................................41
A.1.1. A message from one person to another with simple
addressing .............................................41
A.1.2. Different types of mailboxes ...........................42
A.1.3. Group addresses ........................................43
A.2. Reply messages ...........................................43
A.3. Resent messages ..........................................44
A.4. Messages with trace fields ...............................46
A.5. White space, comments, and other oddities ................47
A.6. Obsoleted forms ..........................................47
A.6.1. Obsolete addressing ....................................48
A.6.2. Obsolete dates .........................................48
A.6.3. Obsolete white space and comments ......................48
Appendix B. Differences from earlier standards ................49
Appendix C. Notices ...........................................50
Full Copyright Statement ......................................51
1. Introduction 1. Introduction
1.1. Scope 1.1. Scope
This standard specifies a syntax for text messages that are sent between This standard specifies a syntax for text messages that are sent
computer users, within the framework of "electronic mail" messages. This between computer users, within the framework of "electronic mail"
standard supersedes the one specified in Request For Comments 822, messages. This standard supersedes the one specified in Request For
"Standard for the Format of ARPA Internet Text Messages" [RFC-822], Comments (RFC) 822, "Standard for the Format of ARPA Internet Text
updating it to reflect current practice and incorporating incremental Messages" [RFC822], updating it to reflect current practice and
changes that were specified in other RFCs [STD-3]. incorporating incremental changes that were specified in other RFCs
[STD3].
This standard specifies a syntax only for text messages. In particular, This standard specifies a syntax only for text messages. In
it makes no provision for the transmission of images, audio, or other particular, it makes no provision for the transmission of images,
sorts of structured data in electronic mail messages. There are several audio, or other sorts of structured data in electronic mail messages.
extensions published, such as the MIME document series [RFC-2045, RFC- There are several extensions published, such as the MIME document
2046, RFC-2049], which describe mechanisms for the transmission of such series [RFC2045, RFC2046, RFC2049], which describe mechanisms for the
data through electronic mail, either by extending the syntax provided transmission of such data through electronic mail, either by
here or by structuring such messages to conform to this syntax. Those extending the syntax provided here or by structuring such messages to
mechanisms are outside of the scope of this standard. conform to this syntax. Those mechanisms are outside of the scope of
this standard.
In the context of electronic mail, messages are viewed as having an In the context of electronic mail, messages are viewed as having an
envelope and contents. The envelope contains whatever information is envelope and contents. The envelope contains whatever information is
needed to accomplish transmission and delivery. (See [SMTP] for a needed to accomplish transmission and delivery. (See [RFC2821] for a
discussion of the envelope.) The contents comprise the object to be discussion of the envelope.) The contents comprise the object to be
delivered to the recipient. This standard applies only to the format and delivered to the recipient. This standard applies only to the format
some of the semantics of message contents. It contains no specification and some of the semantics of message contents. It contains no
of the information in the envelope. specification of the information in the envelope.
However, some message systems may use information from the contents to However, some message systems may use information from the contents
create the envelope. It is intended that this standard facilitate the to create the envelope. It is intended that this standard facilitate
acquisition of such information by programs. the acquisition of such information by programs.
This specification is intended as a definition of what message content This specification is intended as a definition of what message
format is to be passed between systems. Though some message systems content format is to be passed between systems. Though some message
locally store messages in this format (which eliminates the need for systems locally store messages in this format (which eliminates the
translation between formats) and others use formats that differ from the need for translation between formats) and others use formats that
one specified in this standard, local storage is outside of the scope of differ from the one specified in this standard, local storage is
this standard. outside of the scope of this standard.
Note: This standard is not intended to dictate the internal formats used Note: This standard is not intended to dictate the internal formats
by sites, the specific message system features that they are expected to used by sites, the specific message system features that they are
support, or any of the characteristics of user interface programs that expected to support, or any of the characteristics of user interface
create or read messages. In addition, this standard does not specify an programs that create or read messages. In addition, this standard
encoding of the characters for either transport or storage; that is, it does not specify an encoding of the characters for either transport
does not specify the number of bits used or how those bits are or storage; that is, it does not specify the number of bits used or
specifically transferred over the wire or stored on disk. how those bits are specifically transferred over the wire or stored
on disk.
1.2. Notational conventions 1.2. Notational conventions
1.2.1. Requirements notation 1.2.1. Requirements notation
This document occasionally uses terms that appear in capital letters. This document occasionally uses terms that appear in capital letters.
When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD
NOT", and "MAY" appear capitalized, they are being used to indicate NOT", and "MAY" appear capitalized, they are being used to indicate
particular requirements of this specification. A discussion of the particular requirements of this specification. A discussion of the
meanings of these terms appears in [RFC-2119]. meanings of these terms appears in [RFC2119].
1.2.2. Syntactic notation 1.2.2. Syntactic notation
This standard uses the Augmented Backus-Naur Form (ABNF) notation This standard uses the Augmented Backus-Naur Form (ABNF) notation
specified in [RFC-2234] for the formal definitions of the syntax of specified in [RFC2234] for the formal definitions of the syntax of
messages. Characters will be specified either by a decimal value (e.g., messages. Characters will be specified either by a decimal value
the value %d65 for uppercase A and %d97 for lowercase A) or by a case- (e.g., the value %d65 for uppercase A and %d97 for lowercase A) or by
insensitive literal value enclosed in quotation marks (e.g., "A" for a case-insensitive literal value enclosed in quotation marks (e.g.,
either uppercase or lowercase A). See [RFC-2234] for the full "A" for either uppercase or lowercase A). See [RFC2234] for the full
description of the notation. description of the notation.
1.3. Structure of this document 1.3. Structure of this document
This document is divided into several sections. This document is divided into several sections.
This section, section 1, is a short introduction to the document. This section, section 1, is a short introduction to the document.
Section 2 will lay out the general description of a message and its Section 2 lays out the general description of a message and its
constituent parts. This is an overview to help the reader understand constituent parts. This is an overview to help the reader understand
some of the general principles used in the later portions of this some of the general principles used in the later portions of this
document. Any examples in this section MUST NOT be taken as document. Any examples in this section MUST NOT be taken as
specification of the formal syntax of any part of a message. specification of the formal syntax of any part of a message.
Section 3 will specify formal ABNF rules for the structure of each part Section 3 specifies formal ABNF rules for the structure of each part
of a message (syntax) and describe the relationship between those parts of a message (the syntax) and describes the relationship between
and their meaning in the context of a message (the semantics). That is, those parts and their meaning in the context of a message (the
it will describe the actual rules for the structure of each part of a semantics). That is, it describes the actual rules for the structure
message (the syntax) as well as a description of the parts and of each part of a message (the syntax) as well as a description of
instructions on how they ought to be interpreted (the semantics). This the parts and instructions on how they ought to be interpreted (the
will include analysis of the syntax and semantics of subparts of semantics). This includes analysis of the syntax and semantics of
messages that have specific structure. The syntax included in section 3 subparts of messages that have specific structure. The syntax
represents messages as they MUST be created. There are also notes in included in section 3 represents messages as they MUST be created.
section 3 to indicate if any of the options specified in the syntax There are also notes in section 3 to indicate if any of the options
SHOULD be used over any of the others. specified in the syntax SHOULD be used over any of the others.
Both sections 2 and 3 describe messages that are legal to generate for Both sections 2 and 3 describe messages that are legal to generate
purposes of this standard. for purposes of this standard.
Section 4 of this document specifies an "obsolete" syntax. There are Section 4 of this document specifies an "obsolete" syntax. There are
references in section 3 to these obsolete syntactic elements. The rules references in section 3 to these obsolete syntactic elements. The
of the obsolete syntax are elements that have appeared in earlier rules of the obsolete syntax are elements that have appeared in
revisions of this standard or have previously been widely used in earlier revisions of this standard or have previously been widely
Internet messages. As such, these elements MUST be interpreted by used in Internet messages. As such, these elements MUST be
parsers of messages in order to be conformant to this standard. However, interpreted by parsers of messages in order to be conformant to this
since items in this syntax have been determined to be non-interoperable standard. However, since items in this syntax have been determined
or to cause significant problems for recipients of messages, they MUST to be non-interoperable or to cause significant problems for
NOT be generated by creators of conformant messages. recipients of messages, they MUST NOT be generated by creators of
conformant messages.
Section 5 details security considerations to take into account when Section 5 details security considerations to take into account when
implementing this standard. implementing this standard.
Section 6 is a bibliography of references in this document. Section 6 is a bibliography of references in this document.
Section 7 contains the author's address and instructions on where to Section 7 contains the editor's address.
send comments.
Section 8 contains acknowledgements. Section 8 contains acknowledgements.
Appendix A lists examples of different sorts of messages. These examples Appendix A lists examples of different sorts of messages. These
are not exhaustive of the types of messages that appear on the Internet, examples are not exhaustive of the types of messages that appear on
but give a broad overview of certain syntactic forms. the Internet, but give a broad overview of certain syntactic forms.
Appendix B lists the differences between this standard and earlier Appendix B lists the differences between this standard and earlier
standards for Internet messages. standards for Internet messages.
Appendix C has copyright and intellectual property notices. Appendix C has copyright and intellectual property notices.
2. Lexical Analysis of Messages 2. Lexical Analysis of Messages
2.1. General Description 2.1. General Description
At the most basic level, a message is a series of characters. A message At the most basic level, a message is a series of characters. A
that is conformant with this standard is comprised of characters with message that is conformant with this standard is comprised of
values in the range 1 through 127 and interpreted as US-ASCII characters characters with values in the range 1 through 127 and interpreted as
[ASCII]. For brevity, this document sometimes refers to this range of US-ASCII characters [ASCII]. For brevity, this document sometimes
characters as simply "US-ASCII characters". refers to this range of characters as simply "US-ASCII characters".
Note: This standard specifies that messages are made up of characters in Note: This standard specifies that messages are made up of characters
the US-ASCII range of 1 through 127. There are other documents, in the US-ASCII range of 1 through 127. There are other documents,
specifically the MIME document series [RFC-2045, RFC-2046, RFC-2047, specifically the MIME document series [RFC2045, RFC2046, RFC2047,
RFC-2048, RFC-2049], that extend this standard to allow for values RFC2048, RFC2049], that extend this standard to allow for values
outside of that range. Discussion of those mechanisms is not within the outside of that range. Discussion of those mechanisms is not within
scope of this standard. the scope of this standard.
Messages are divided into lines of characters. A line is a series of Messages are divided into lines of characters. A line is a series of
characters that is delimited with the two characters carriage-return and characters that is delimited with the two characters carriage-return
line-feed; that is, the carriage return (CR) character (ASCII value 13) and line-feed; that is, the carriage return (CR) character (ASCII
followed immediately by the line feed (LF) character (ASCII value 10). value 13) followed immediately by the line feed (LF) character (ASCII
(The carriage-return/line-feed pair is usually written in this document value 10). (The carriage-return/line-feed pair is usually written in
as "CRLF".) Each line of characters MUST be limited to 998 characters, this document as "CRLF".)
and SHOULD be limited to 78 characters, excluding the CRLF.
Note: The 998 character limit is due to limitations in many A message consists of header fields (collectively called "the header
implementations which send, receive, or store Internet Message Format of the message") followed, optionally, by a body. The header is a
messages that simply cannot handle more than 998 characters on a line. sequence of lines of characters with special syntax as defined in
The 78 character recommendation is due to limitations in many this standard. The body is simply a sequence of characters that
implementations that display these messages which may truncate the follows the header and is separated from the header by an empty line
display of more than 78 characters per line. Of course, even though (i.e., a line with nothing preceding the CRLF).
these limitations are put on messages, interpreters of messages would do
well to handle an arbitrarily large number of characters in a line,
including for display, for robustness' sake.
A message consists of header fields (collectively called "the header of 2.1.1. Line Length Limits
the message") followed, optionally, by a body. The header is a sequence
of lines of characters with special syntax as defined in this standard. There are two limits that this standard places on the number of
The body is simply a sequence of characters that follows the header and characters in a line. Each line of characters MUST be no more than
is separated from the header by an empty line (i.e., a line with nothing 998 characters, and SHOULD be no more than 78 characters, excluding
preceding the CRLF). the CRLF.
The 998 character limit is due to limitations in many implementations
which send, receive, or store Internet Message Format messages that
simply cannot handle more than 998 characters on a line. Receiving
implementations would do well to handle an arbitrarily large number
of characters in a line for robustness sake. However, there are so
many implementations which (in compliance with the transport
requirements of [RFC2821]) do not accept messages containing more
than 1000 character including the CR and LF per line, it is important
for implementations not to create such messages.
The more conservative 78 character recommendation is to accommodate
the many implementations of user interfaces that display these
messages which may truncate, or disastrously wrap, the display of
more than 78 characters per line, in spite of the fact that such
implementations are non-conformant to the intent of this
specification (and that of [RFC2821] if they actually cause
information to be lost). Again, even though this limitation is put on
messages, it is encumbant upon implementations which display messages
to handle an arbitrarily large number of characters in a line
(certainly at least up to the 998 character limit) for the sake of
robustness.
2.2. Header Fields 2.2. Header Fields
Header fields are lines composed of a field name, followed by a colon Header fields are lines composed of a field name, followed by a colon
(":"), followed by a field body, and terminated by CRLF. A field name (":"), followed by a field body, and terminated by CRLF. A field
MUST be composed of printable US-ASCII characters (i.e., characters that name MUST be composed of printable US-ASCII characters (i.e.,
have values between 33 and 126, inclusive), except colon. A field body characters that have values between 33 and 126, inclusive), except
may be composed of any US-ASCII characters, except for CR and LF. colon. A field body may be composed of any US-ASCII characters,
However, a field body may contain CRLF when used in header "folding" and except for CR and LF. However, a field body may contain CRLF when
"unfolding" as described in section 2.2.3. All field bodies MUST conform used in header "folding" and "unfolding" as described in section
to the syntax described in sections 3 and 4 of this standard. 2.2.3. All field bodies MUST conform to the syntax described in
sections 3 and 4 of this standard.
2.2.1. Unstructured Header Field Bodies 2.2.1. Unstructured Header Field Bodies
Some field bodies in this standard are defined simply as "unstructured" Some field bodies in this standard are defined simply as
(which is specified below as any US-ASCII characters, except for CR and "unstructured" (which is specified below as any US-ASCII characters,
LF) with no further restrictions. These are referred to as unstructured except for CR and LF) with no further restrictions. These are
field bodies. Semantically, unstructured field bodies are simply to be referred to as unstructured field bodies. Semantically, unstructured
treated as a single line of characters with no further processing field bodies are simply to be treated as a single line of characters
(except for header "folding" and "unfolding" as described in section with no further processing (except for header "folding" and
2.2.3). "unfolding" as described in section 2.2.3).
2.2.2. Structured Header Field Bodies 2.2.2. Structured Header Field Bodies
Some field bodies in this standard have specific syntactical structure Some field bodies in this standard have specific syntactical
more restrictive than the unstructured field bodies described above. structure more restrictive than the unstructured field bodies
These are referred to as "structured" field bodies. Structured field described above. These are referred to as "structured" field bodies.
bodies are sequences of specific lexical tokens as described in sections Structured field bodies are sequences of specific lexical tokens as
3 and 4 of this standard. Many of these tokens are allowed (according to described in sections 3 and 4 of this standard. Many of these tokens
their syntax) to be introduced or end with comments (as described in are allowed (according to their syntax) to be introduced or end with
section 3.2.3) as well as the space (SP, ASCII value 32) and horizontal comments (as described in section 3.2.3) as well as the space (SP,
tab (HTAB, ASCII value 9) characters (together known as the white space ASCII value 32) and horizontal tab (HTAB, ASCII value 9) characters
characters, WSP), and those WSP characters are subject to header (together known as the white space characters, WSP), and those WSP
"folding" and "unfolding" as described in section 2.2.3. Semantic characters are subject to header "folding" and "unfolding" as
analysis of structured field bodies is given along with their syntax. described in section 2.2.3. Semantic analysis of structured field
bodies is given along with their syntax.
2.2.3. Long Header Fields 2.2.3. Long Header Fields
Each header field is logically a single line of characters comprising Each header field is logically a single line of characters comprising
the field name, the colon, and the field body. For convenience however, the field name, the colon, and the field body. For convenience
and to deal with the 998/78 character limitations per line, the field however, and to deal with the 998/78 character limitations per line,
body portion of a header field can be split into a multiple line the field body portion of a header field can be split into a multiple
representation; this is called "folding". The general rule is that line representation; this is called "folding". The general rule is
wherever this standard allows for folding white space (not simply WSP that wherever this standard allows for folding white space (not
characters), a CRLF may be inserted before any WSP. For example, the simply WSP characters), a CRLF may be inserted before any WSP. For
header field: example, the header field:
Subject: This is a test Subject: This is a test
can be represented as: can be represented as:
Subject: This Subject: This
is a test is a test
Note: Though structured field bodies are defined in such a way that Note: Though structured field bodies are defined in such a way that
folding can take place between many of the lexical tokens (and even folding can take place between many of the lexical tokens (and even
within some of the lexical tokens), folding SHOULD be limited to placing within some of the lexical tokens), folding SHOULD be limited to
the CRLF at higher-level syntactic breaks. For instance, if a field body placing the CRLF at higher-level syntactic breaks. For instance, if
is defined as comma-separated values, it is recommended that folding a field body is defined as comma-separated values, it is recommended
occur after the comma separating the structured items in preference to that folding occur after the comma separating the structured items in
other places where the field could be folded, even if it is allowed preference to other places where the field could be folded, even if
elsewhere. it is allowed elsewhere.
The process of moving from this folded multiple-line representation of a The process of moving from this folded multiple-line representation
header field to its single line representation is called "unfolding". of a header field to its single line representation is called
Unfolding is accomplished by simply removing any CRLF that is "unfolding". Unfolding is accomplished by simply removing any CRLF
immediately followed by WSP. Each header field should be treated in its that is immediately followed by WSP. Each header field should be
unfolded form for further syntactic and semantic evaluation. treated in its unfolded form for further syntactic and semantic
evaluation.
2.3. Body 2.3. Body
The body of a message is simply lines of US-ASCII characters. The only The body of a message is simply lines of US-ASCII characters. The
two limitations on the body are as follows: only two limitations on the body are as follows:
- CR and LF MUST only occur together as CRLF; they MUST NOT appear - CR and LF MUST only occur together as CRLF; they MUST NOT appear
independently in the body. independently in the body.
- Lines of characters in the body MUST be limited to 998 characters, and - Lines of characters in the body MUST be limited to 998 characters,
SHOULD be limited to 78 characters, excluding the CRLF. and SHOULD be limited to 78 characters, excluding the CRLF.
Note: As was stated earlier, there are other standards documents, Note: As was stated earlier, there are other standards documents,
specifically the MIME documents [RFC-2045, RFC-2046, RFC-2048, RFC-2049] specifically the MIME documents [RFC2045, RFC2046, RFC2048, RFC2049]
that extend this standard to allow for different sorts of message that extend this standard to allow for different sorts of message
bodies. Again, these mechanisms are beyond the scope of this document. bodies. Again, these mechanisms are beyond the scope of this
document.
3. Syntax 3. Syntax
3.1. Introduction 3.1. Introduction
The syntax as given in this section defines the legal syntax of Internet The syntax as given in this section defines the legal syntax of
messages. Messages that are conformant to this standard MUST conform to Internet messages. Messages that are conformant to this standard
the syntax in this section. If there are options in this section where MUST conform to the syntax in this section. If there are options in
one option SHOULD be generated, that is indicated either in the prose or this section where one option SHOULD be generated, that is indicated
in a comment next to the syntax. either in the prose or in a comment next to the syntax.
For the defined expressions, a short description of the syntax and use For the defined expressions, a short description of the syntax and
is given, followed by the syntax in ABNF, followed by a semantic use is given, followed by the syntax in ABNF, followed by a semantic
analysis. Primitive tokens that are used but otherwise unspecified come analysis. Primitive tokens that are used but otherwise unspecified
from [RFC-2234]. come from [RFC2234].
In some of the definitions, there will be nonterminals whose names start In some of the definitions, there will be nonterminals whose names
with "obs-". These "obs-" elements refer to tokens defined in the start with "obs-". These "obs-" elements refer to tokens defined in
obsolete syntax in section 4. In all cases, these productions are to be the obsolete syntax in section 4. In all cases, these productions
ignored for the purposes of generating legal Internet messages and MUST are to be ignored for the purposes of generating legal Internet
NOT be used as part of such a message. However, when interpreting messages and MUST NOT be used as part of such a message. However,
messages, these tokens MUST be honored as part of the legal syntax. In when interpreting messages, these tokens MUST be honored as part of
this sense, section 3 defines a grammar for generation of messages, with the legal syntax. In this sense, section 3 defines a grammar for
"obs-" elements that are to be ignored, while section 4 adds grammar for generation of messages, with "obs-" elements that are to be ignored,
interpretation of messages. while section 4 adds grammar for interpretation of messages.
3.2. Lexical Tokens 3.2. Lexical Tokens
The following rules are used to define an underlying lexical analyzer, The following rules are used to define an underlying lexical
which feeds tokens to the higher-level parsers. This section defines the analyzer, which feeds tokens to the higher-level parsers. This
tokens used in structured header field bodies. section defines the tokens used in structured header field bodies.
Note: Readers of this standard need to pay special attention to how Note: Readers of this standard need to pay special attention to how
these lexical tokens are used in both the lower-level and higher-level these lexical tokens are used in both the lower-level and
syntax later in the document. Particularly, the white space tokens and higher-level syntax later in the document. Particularly, the white
the comment tokens defined in section 3.2.3 get used in the lower-level space tokens and the comment tokens defined in section 3.2.3 get used
tokens defined here, and those lower-level tokens are in turn used as in the lower-level tokens defined here, and those lower-level tokens
parts of the higher-level tokens defined later. Therefore, the white are in turn used as parts of the higher-level tokens defined later.
space and comments may be allowed in the higher-level tokens even though Therefore, the white space and comments may be allowed in the
they may not explicitly appear in a particular definition. higher-level tokens even though they may not explicitly appear in a
particular definition.
3.2.1. Primitive Tokens 3.2.1. Primitive Tokens
The following are primitive tokens referred to elsewhere in this The following are primitive tokens referred to elsewhere in this
standard, but not otherwise defined in [RFC-2234]. Some of them will not standard, but not otherwise defined in [RFC2234]. Some of them will
appear anywhere else in the syntax, but they are convenient to refer to not appear anywhere else in the syntax, but they are convenient to
in other parts of this document. refer to in other parts of this document.
Note: The "specials" below are just such an example. Though the specials Note: The "specials" below are just such an example. Though the
token does not appear anywhere else in this standard, it is useful for specials token does not appear anywhere else in this standard, it is
implementers who use tools that lexically analyze messages. Each of the useful for implementers who use tools that lexically analyze
characters in specials can be used to indicate a tokenization point in messages. Each of the characters in specials can be used to indicate
lexical analysis. a tokenization point in lexical analysis.
NO-WS-CTL = %d1-8 / ; US-ASCII control characters NO-WS-CTL = %d1-8 / ; US-ASCII control characters
%d11 / ; that do not include the %d11 / ; that do not include the
%d12 / ; carriage return, line feed, %d12 / ; carriage return, line feed,
%d14-31 / ; and white space characters %d14-31 / ; and white space characters
%d127 %d127
text = %d1-9 / ; Characters excluding CR and LF text = %d1-9 / ; Characters excluding CR and LF
%d11-12 / %d11 /
%d12 /
%d14-127 / %d14-127 /
obs-text obs-text
specials = "(" / ")" / ; Special characters used in specials = "(" / ")" / ; Special characters used in
"<" / ">" / ; other parts of the syntax "<" / ">" / ; other parts of the syntax
"[" / "]" / "[" / "]" /
":" / ";" / ":" / ";" /
"@" / "\" / "@" / "\" /
"," / "." / "," / "." /
DQUOTE DQUOTE
No special semantics are attached to these tokens. They are simply No special semantics are attached to these tokens. They are simply
single characters. single characters.
3.2.2. Quoted characters 3.2.2. Quoted characters
Some characters are reserved for special interpretation, such as Some characters are reserved for special interpretation, such as
delimiting lexical tokens. To permit use of these characters as delimiting lexical tokens. To permit use of these characters as
uninterpreted data, a quoting mechanism is provided. uninterpreted data, a quoting mechanism is provided.
quoted-pair = ("\" text) / obs-qp quoted-pair = ("\" text) / obs-qp
Where any quoted-pair appears, it is to be interpreted as the text Where any quoted-pair appears, it is to be interpreted as the text
character alone. That is to say, the "\" character that appears as part character alone. That is to say, the "\" character that appears as
of a quoted-pair is semantically "invisible". part of a quoted-pair is semantically "invisible".
Note: The "\" character may appear in a message where it is not part of Note: The "\" character may appear in a message where it is not part
a quoted-pair. A "\" character that does not appear in a quoted-pair is of a quoted-pair. A "\" character that does not appear in a
not semantically invisible. The only places in this standard where quoted-pair is not semantically invisible. The only places in this
quoted-pair currently appears are ccontent, qcontent, dcontent, no-fold- standard where quoted-pair currently appears are ccontent, qcontent,
quote, and no-fold-literal. dcontent, no-fold-quote, and no-fold-literal.
3.2.3. Folding white space and comments 3.2.3. Folding white space and comments
White space characters, including white space used in folding (described White space characters, including white space used in folding
in section 2.2.3), may appear between many elements in header field (described in section 2.2.3), may appear between many elements in
bodies. Also, strings of characters that are treated as comments may be header field bodies. Also, strings of characters that are treated as
included in structured field bodies as characters enclosed in comments may be included in structured field bodies as characters
parenthesis. The following defines the folding white space (FWS) and enclosed in parentheses. The following defines the folding white
comment contructs. space (FWS) and comment constructs.
Strings of characters enclosed in parentheses are considered comments so Strings of characters enclosed in parentheses are considered comments
long as they do not appear within a "quoted-string", as defined in so long as they do not appear within a "quoted-string", as defined in
section 3.2.5. Comments may nest. section 3.2.5. Comments may nest.
There are several places in this standard where comments and FWS may be There are several places in this standard where comments and FWS may
freely inserted. To accommodate that syntax, an additional token for be freely inserted. To accommodate that syntax, an additional token
"CFWS" is defined for places where comments and/or FWS can occur. for "CFWS" is defined for places where comments and/or FWS can occur.
However, where CFWS occurs in this standard, it MUST NOT be inserted in However, where CFWS occurs in this standard, it MUST NOT be inserted
such a way that any line of a folded header field is made up entirely of in such a way that any line of a folded header field is made up
WSP characters and nothing else. entirely of WSP characters and nothing else.
FWS = ([*WSP CRLF] 1*WSP) / ; Folding white space FWS = ([*WSP CRLF] 1*WSP) / ; Folding white space
obs-FWS obs-FWS
ctext = NO-WS-CTL / ; Non white space controls ctext = NO-WS-CTL / ; Non white space controls
%d33-39 / ; The rest of the US-ASCII %d33-39 / ; The rest of the US-ASCII
%d42-91 / ; characters not including "(", %d42-91 / ; characters not including "(",
%d93-126 ; ")", or "\" %d93-126 ; ")", or "\"
ccontent = ctext / quoted-pair / comment ccontent = ctext / quoted-pair / comment
comment = "(" *([FWS] ccontent) [FWS] ")" comment = "(" *([FWS] ccontent) [FWS] ")"
CFWS = *([FWS] comment) [FWS] CFWS = *([FWS] comment) (([FWS] comment) / FWS)
Throughout this standard, where FWS (the folding white space token) Throughout this standard, where FWS (the folding white space token)
appears, it indicates a place where header folding, as discussed in appears, it indicates a place where header folding, as discussed in
section 2.2.3, may take place. Wherever header folding appears in a section 2.2.3, may take place. Wherever header folding appears in a
message (that is, a header field body containing a CRLF followed by any message (that is, a header field body containing a CRLF followed by
WSP), header unfolding (removal of the CRLF) is performed before any any WSP), header unfolding (removal of the CRLF) is performed before
further lexical analysis is performed on that header field according to any further lexical analysis is performed on that header field
this standard. That is to say, any CRLF that appears in FWS is according to this standard. That is to say, any CRLF that appears in
semantically "invisible." FWS is semantically "invisible."
A comment is normally used in a structured field body to provide some A comment is normally used in a structured field body to provide some
human readable informational text. Since a comment is allowed to contain human readable informational text. Since a comment is allowed to
FWS, folding is permitted within the comment. Also note that since contain FWS, folding is permitted within the comment. Also note that
quoted-pair is allowed in a comment, the parentheses and backslash since quoted-pair is allowed in a comment, the parentheses and
characters may appear in a comment so long as they appear as a quoted- backslash characters may appear in a comment so long as they appear
pair. Semantically, the enclosing parentheses are not part of the as a quoted-pair. Semantically, the enclosing parentheses are not
comment; the comment is what is contained between the two parentheses. part of the comment; the comment is what is contained between the two
As stated earlier, the "\" in any quoted-pair and the CRLF in any FWS parentheses. As stated earlier, the "\" in any quoted-pair and the
that appears within the comment are semantically "invisible" and CRLF in any FWS that appears within the comment are semantically
therefore not part of the comment either. "invisible" and therefore not part of the comment either.
Runs of FWS, comment or CFWS that occur between lexical tokens in a Runs of FWS, comment or CFWS that occur between lexical tokens in a
structured field header are semantically interpreted as a single space structured field header are semantically interpreted as a single
character. space character.
3.2.4. Atom 3.2.4. Atom
Several productions in structured header field bodies are simply strings Several productions in structured header field bodies are simply
of certain basic characters. Such productions are called atoms. strings of certain basic characters. Such productions are called
atoms.
Some of the structured header field bodies also allow the period Some of the structured header field bodies also allow the period
character (".", ASCII value 46) within runs of atext. An additional character (".", ASCII value 46) within runs of atext. An additional
"dot-atom" token is defined for those purposes. "dot-atom" token is defined for those purposes.
atext = ALPHA / DIGIT / ; Any character except controls, atext = ALPHA / DIGIT / ; Any character except controls,
"!" / "#" / ; SP, and specials. "!" / "#" / ; SP, and specials.
"$" / "%" / ; Used for atoms "$" / "%" / ; Used for atoms
"&" / "'" / "&" / "'" /
"*" / "+" / "*" / "+" /
"-" / "/" / "-" / "/" /
"=" / "?" / "=" / "?" /
"^" / "_" / "^" / "_" /
"`" / "{" / "`" / "{" /
"|" / "}" / "|" / "}" /
"~" "~"
atom = [CFWS] 1*atext [CFWS] atom = [CFWS] 1*atext [CFWS]
dot-atom = [CFWS] dot-atom-text [CFWS] dot-atom = [CFWS] dot-atom-text [CFWS]
dot-atom-text = 1*atext *("." 1*atext) dot-atom-text = 1*atext *("." 1*atext)
Both atom and dot-atom are interpreted as a single unit, comprised of Both atom and dot-atom are interpreted as a single unit, comprised of
the string of characters that make it up. Semantically, the optional the string of characters that make it up. Semantically, the optional
comments and FWS surrounding the rest of the characters are not part of comments and FWS surrounding the rest of the characters are not part
the atom; the atom is only the run of atext characters in an atom, or of the atom; the atom is only the run of atext characters in an atom,
the atext and "." characters in a dot-atom. or the atext and "." characters in a dot-atom.
3.2.5. Quoted strings 3.2.5. Quoted strings
Strings of characters that include characters other than those allowed Strings of characters that include characters other than those
in atoms may be represented in a quoted string format, where the allowed in atoms may be represented in a quoted string format, where
characters are surrounded by quote (DQUOTE, ASCII value 34) characters. the characters are surrounded by quote (DQUOTE, ASCII value 34)
characters.
qtext = NO-WS-CTL / ; Non white space controls qtext = NO-WS-CTL / ; Non white space controls
%d33 / ; The rest of the US-ASCII %d33 / ; The rest of the US-ASCII
%d35-91 / ; characters not including "\" %d35-91 / ; characters not including "\"
%d93-126 ; or the quote character %d93-126 ; or the quote character
qcontent = qtext / quoted-pair qcontent = qtext / quoted-pair
quoted-string = [CFWS] quoted-string = [CFWS]
DQUOTE *([FWS] qcontent) [FWS] DQUOTE DQUOTE *([FWS] qcontent) [FWS] DQUOTE
[CFWS] [CFWS]
A quoted-string is treated as a unit. That is, quoted-string is A quoted-string is treated as a unit. That is, quoted-string is
identical to atom, semantically. Since a quoted-string is allowed to identical to atom, semantically. Since a quoted-string is allowed to
contain FWS, folding is permitted. Also note that since quoted-pair is contain FWS, folding is permitted. Also note that since quoted-pair
allowed in a quoted-string, the quote and backslash characters may is allowed in a quoted-string, the quote and backslash characters may
appear in a quoted-string so long as they appear as a quoted-pair. appear in a quoted-string so long as they appear as a quoted-pair.
Semantically, neither the optional CFWS outside of the quote characters Semantically, neither the optional CFWS outside of the quote
nor the quote characters themselves are part of the quoted-string; the characters nor the quote characters themselves are part of the
quoted-string is what is contained between the two quote characters. As quoted-string; the quoted-string is what is contained between the two
stated earlier, the "\" in any quoted-pair and the CRLF in any FWS/CFWS quote characters. As stated earlier, the "\" in any quoted-pair and
that appears within the quoted-string are semantically "invisible" and the CRLF in any FWS/CFWS that appears within the quoted-string are
therefore not part of the quoted-string either. semantically "invisible" and therefore not part of the quoted-string
either.
3.2.6. Miscellaneous tokens 3.2.6. Miscellaneous tokens
Three additional tokens are defined, word and phrase for combinations of Three additional tokens are defined, word and phrase for combinations
atoms and/or quoted-strings, and unstructured for use in unstructured of atoms and/or quoted-strings, and unstructured for use in
header fields and in some places within structured header fields. unstructured header fields and in some places within structured
header fields.
word = atom / quoted-string word = atom / quoted-string
phrase = 1*word / obs-phrase phrase = 1*word / obs-phrase
utext = NO-WS-CTL / ; Non white space controls utext = NO-WS-CTL / ; Non white space controls
%d33-126 / ; The rest of US-ASCII %d33-126 / ; The rest of US-ASCII
obs-utext obs-utext
unstructured = *([FWS] utext) [FWS] unstructured = *([FWS] utext) [FWS]
3.3. Date and Time Specification 3.3. Date and Time Specification
Date and time occur in several header fields. This section specifies the Date and time occur in several header fields. This section specifies
syntax for a full date and time specification. Though folding white the syntax for a full date and time specification. Though folding
space is permitted throughout the date-time specification, it is white space is permitted throughout the date-time specification, it
recommended that only a single space be used where FWS is required and is RECOMMENDED that a single space be used in each place that FWS
no space be used where FWS is optional in the date-time specification; appears (whether it is required or optional); some older
some older implementations may not interpret other occurrences of implementations may not interpret other occurrences of folding white
folding white space correctly. space correctly.
date-time = [ day-of-week "," ] date FWS time [CFWS] date-time = [ day-of-week "," ] date FWS time [CFWS]
day-of-week = ([FWS] day-name) / obs-day-of-week day-of-week = ([FWS] day-name) / obs-day-of-week
day-name = "Mon" / "Tue" / "Wed" / "Thu" / day-name = "Mon" / "Tue" / "Wed" / "Thu" /
"Fri" / "Sat" / "Sun" "Fri" / "Sat" / "Sun"
date = day month year date = day month year
skipping to change at line 573 skipping to change at page 15, line 4
time-of-day = hour ":" minute [ ":" second ] time-of-day = hour ":" minute [ ":" second ]
hour = 2DIGIT / obs-hour hour = 2DIGIT / obs-hour
minute = 2DIGIT / obs-minute minute = 2DIGIT / obs-minute
second = 2DIGIT / obs-second second = 2DIGIT / obs-second
zone = (( "+" / "-" ) 4DIGIT) / obs-zone zone = (( "+" / "-" ) 4DIGIT) / obs-zone
The day is the numeric day of the month. The year is any numeric
year 1900 or later.
The day is the numeric day of the month. The year is any numeric year The time-of-day specifies the number of hours, minutes, and
1900 or later. optionally seconds since midnight of the date indicated.
The time-of-day specifies the number of hours, minutes, and optionally
seconds since midnight of the date indicated.
The date and time-of-day SHOULD express local time. The date and time-of-day SHOULD express local time.
The zone specifies the offset from Coordinated Universal Time (UTC, The zone specifies the offset from Coordinated Universal Time (UTC,
formerly referred to as "Greenwich Mean Time") that the date and time- formerly referred to as "Greenwich Mean Time") that the date and
of-day represent. The "+" or "-" indicates whether the time-of-day is time-of-day represent. The "+" or "-" indicates whether the
ahead of (i.e., east of) or behind (i.e., west of) Universal Time. The time-of-day is ahead of (i.e., east of) or behind (i.e., west of)
first two digits indicate the number of hours difference from Universal Universal Time. The first two digits indicate the number of hours
Time, and the last two digits indicate the number of minutes difference difference from Universal Time, and the last two digits indicate the
from Universal Time. (Hence, +hhmm means +(hh * 60 + mm) minutes, and - number of minutes difference from Universal Time. (Hence, +hhmm
hhmm means -(hh * 60 + mm) minutes). The form "+0000" SHOULD be used to means +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm)
indicate a time zone at Universal Time. Though "-0000" also indicates minutes). The form "+0000" SHOULD be used to indicate a time zone at
Universal Time, it is used to indicate that the time was generated on a Universal Time. Though "-0000" also indicates Universal Time, it is
system that may be in a local time zone other than Universal Time and used to indicate that the time was generated on a system that may be
therefore indicates that the date-time contains no information about the in a local time zone other than Universal Time and therefore
local time zone. indicates that the date-time contains no information about the local
time zone.
A date-time specification MUST be semantically valid. That is, the day- A date-time specification MUST be semantically valid. That is, the
of-the week (if included) MUST be the day implied by the date, the day-of-the-week (if included) MUST be the day implied by the date,
numeric day-of-month MUST be between 1 and the number of days allowed the numeric day-of-month MUST be between 1 and the number of days
for the specified month (in the specified year), the time-of-day MUST be allowed for the specified month (in the specified year), the
in the range 00:00:00 through 23:59:60 (the number of seconds allowing time-of-day MUST be in the range 00:00:00 through 23:59:60 (the
for a leap second; see [STD-12]), and the zone MUST be within the range number of seconds allowing for a leap second; see [STD12]), and the
-9959 through +9959. zone MUST be within the range -9959 through +9959.
3.4. Address Specification 3.4. Address Specification
Addresses occur in several message header fields to indicate senders and Addresses occur in several message header fields to indicate senders
recipients of messages. An address may either be an individual mailbox, and recipients of messages. An address may either be an individual
or a group of mailboxes. mailbox, or a group of mailboxes.
address = mailbox / group address = mailbox / group
mailbox = name-addr / addr-spec / obs-mailbox mailbox = name-addr / addr-spec
name-addr = [display-name] [CFWS] "<" addr-spec ">" [CFWS] name-addr = [display-name] angle-addr
angle-addr = [CFWS] "<" addr-spec ">" [CFWS] / obs-angle-addr
group = display-name ":" [mailbox-list / CFWS] ";" group = display-name ":" [mailbox-list / CFWS] ";"
[CFWS] [CFWS]
display-name = phrase display-name = phrase
mailbox-list = (mailbox *("," mailbox)) / obs-mbox-list mailbox-list = (mailbox *("," mailbox)) / obs-mbox-list
address-list = address *("," address) / obs-addr-list address-list = (address *("," address)) / obs-addr-list
A mailbox receives mail. It is a conceptual entity which does not A mailbox receives mail. It is a conceptual entity which does not
necessarily pertain to file storage. For example, some sites may choose necessarily pertain to file storage. For example, some sites may
to print mail on a printer and deliver the output to the addressee's choose to print mail on a printer and deliver the output to the
desk. Normally, a mailbox is comprised of two parts: (1) an optional addressee's desk. Normally, a mailbox is comprised of two parts: (1)
display name that indicates the name of the recipient (which could be a an optional display name that indicates the name of the recipient
person or a system) that could be displayed to the user of a mail (which could be a person or a system) that could be displayed to the
application, and (2) an addr-spec address enclosed in angle brackets user of a mail application, and (2) an addr-spec address enclosed in
("<" and ">"). There is also an alternate simple form of a mailbox where angle brackets ("<" and ">"). There is also an alternate simple form
the addr-spec address appears alone, without the recipient's name or the of a mailbox where the addr-spec address appears alone, without the
angle brackets. The Internet addr-spec address is described in section recipient's name or the angle brackets. The Internet addr-spec
3.4.1. address is described in section 3.4.1.
Note: Some legacy implementations used the simple form where the addr- Note: Some legacy implementations used the simple form where the
spec appears without the angle brackets, but included the name of the addr-spec appears without the angle brackets, but included the name
recipient in parentheses as a comment following the addr-spec. Since the of the recipient in parentheses as a comment following the addr-spec.
meaning of the information in a comment is unspecified, implementations Since the meaning of the information in a comment is unspecified,
SHOULD use the full name-addr for of the mailbox, instead of the legacy implementations SHOULD use the full name-addr form of the mailbox,
form, to specify the display name associated with a mailbox. Also, instead of the legacy form, to specify the display name associated
because some legacy implementations interpret the comment, comments with a mailbox. Also, because some legacy implementations interpret
generally SHOULD NOT be used in address fields to avoid confusing such the comment, comments generally SHOULD NOT be used in address fields
implementations. to avoid confusing such implementations.
When it is desirable to treat several mailboxes as a single unit (i.e., When it is desirable to treat several mailboxes as a single unit
in a distribution list), the group construct can be used. The group (i.e., in a distribution list), the group construct can be used. The
construct allows the sender to indicate a named group of recipients. group construct allows the sender to indicate a named group of
This is done by giving a display name for the group, followed by a recipients. This is done by giving a display name for the group,
colon, followed by a comma separated list of any number of mailboxes followed by a colon, followed by a comma separated list of any number
(including zero and one), and ending with a semicolon. Because the list of mailboxes (including zero and one), and ending with a semicolon.
of mailboxes can be empty, using the group construct is also a simple Because the list of mailboxes can be empty, using the group construct
way to communicate to recipients that the message was sent to one or is also a simple way to communicate to recipients that the message
more named sets of recipients, without actually providing the individual was sent to one or more named sets of recipients, without actually
mailbox address for each of those recipients. providing the individual mailbox address for each of those
recipients.
3.4.1. Addr-spec specification 3.4.1. Addr-spec specification
An addr-spec is a specific Internet identifier that contains a locally An addr-spec is a specific Internet identifier that contains a
interpreted string followed by the at-sign character ("@", ASCII value locally interpreted string followed by the at-sign character ("@",
64) followed by an Internet domain. The locally interpreted string is ASCII value 64) followed by an Internet domain. The locally
either a quoted-string or a dot-atom. If the string can be represented interpreted string is either a quoted-string or a dot-atom. If the
as a dot-atom (that is, it contains no characters other than atext string can be represented as a dot-atom (that is, it contains no
characters or "." surrounded by atext characters), then the dot-atom characters other than atext characters or "." surrounded by atext
form SHOULD be used and the quoted-string form SHOULD NOT be used. characters), then the dot-atom form SHOULD be used and the
Comments and folding white space SHOULD NOT be used around the "@" in quoted-string form SHOULD NOT be used. Comments and folding white
the addr-spec. space SHOULD NOT be used around the "@" in the addr-spec.
addr-spec = local-part "@" domain addr-spec = local-part "@" domain
local-part = dot-atom / quoted-string / obs-local-part local-part = dot-atom / quoted-string / obs-local-part
domain = dot-atom / domain-literal / obs-domain domain = dot-atom / domain-literal / obs-domain
domain-literal = [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS] domain-literal = [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS]
dcontent = dtext / quoted-pair dcontent = dtext / quoted-pair
dtext = NO-WS-CTL / ; Non white space controls dtext = NO-WS-CTL / ; Non white space controls
%d33-90 / ; The rest of the US-ASCII %d33-90 / ; The rest of the US-ASCII
%d94-126 ; characters not including "[", %d94-126 ; characters not including "[",
; "]", or "\" ; "]", or "\"
The domain portion identifies the point to which the mail is delivered. The domain portion identifies the point to which the mail is
In the dot-atom form, this is interpreted as an Internet domain name delivered. In the dot-atom form, this is interpreted as an Internet
(either a host name or a mail exchanger name) as described in [STD-3, domain name (either a host name or a mail exchanger name) as
STD-13, STD-14]. In the domain-literal form, the domain is interpreted described in [STD3, STD13, STD14]. In the domain-literal form, the
as the literal Internet address of the particular host. In both cases, domain is interpreted as the literal Internet address of the
how addressing is used and how messages are transported to a particular particular host. In both cases, how addressing is used and how
host is covered in the mail transport document [SMTP]. These mechanisms messages are transported to a particular host is covered in the mail
are outside of the scope of this document. transport document [RFC2821]. These mechanisms are outside of the
scope of this document.
The local-part portion is a domain dependent string. In addresses, it is The local-part portion is a domain dependent string. In addresses,
simply interpreted on the particular host as a name of a particular it is simply interpreted on the particular host as a name of a
mailbox. particular mailbox.
3.5 Overall message syntax 3.5 Overall message syntax
A message consists of header fields, optionally followed by a message A message consists of header fields, optionally followed by a message
body. Lines in a message MUST be a maximum of 998 characters excluding body. Lines in a message MUST be a maximum of 998 characters
the CRLF, but it is RECOMMENDED that lines be limited to 78 characters excluding the CRLF, but it is RECOMMENDED that lines be limited to 78
excluding the CRLF. (See the note in section 2.1 for explanation.) In a characters excluding the CRLF. (See section 2.1.1 for explanation.)
message body, though all of the characters listed in the text rule MAY In a message body, though all of the characters listed in the text
be used, the use of US-ASCII control characters (values 1 through 8, 11, rule MAY be used, the use of US-ASCII control characters (values 1
12, and 14 through 31) is discouraged since their interpretation by through 8, 11, 12, and 14 through 31) is discouraged since their
receivers for display is not guaranteed. interpretation by receivers for display is not guaranteed.
message = (fields / obs-fields) message = (fields / obs-fields)
[CRLF body] [CRLF body]
body = *(*998text CRLF) *998text body = *(*998text CRLF) *998text
The header fields carry most of the semantic information and are defined The header fields carry most of the semantic information and are
in section 3.6. The body is simply a series of lines of text which are defined in section 3.6. The body is simply a series of lines of text
uninterpreted for the purposes of this standard. which are uninterpreted for the purposes of this standard.
3.6. Field definitions 3.6. Field definitions
The header fields of a message are defined here. All header fields have The header fields of a message are defined here. All header fields
the same general syntactic structure: A field name, followed by a colon, have the same general syntactic structure: A field name, followed by
followed by the field body. The specific syntax for each header field is a colon, followed by the field body. The specific syntax for each
defined in the subsequent sections. header field is defined in the subsequent sections.
Note: In the ABNF syntax for each field in subsequent sections, each Note: In the ABNF syntax for each field in subsequent sections, each
field name is followed by the required colon. However, for brevity field name is followed by the required colon. However, for brevity
sometimes the colon is not referred to in the textual description of the sometimes the colon is not referred to in the textual description of
syntax. It is, nonetheless, required. the syntax. It is, nonetheless, required.
It is important to note that the header fields are not guaranteed to be It is important to note that the header fields are not guaranteed to
in a particular order. They may appear in any order, and they have been be in a particular order. They may appear in any order, and they
known to be reordered occasionally when transported over the Internet. have been known to be reordered occasionally when transported over
However, for the purposes of this standard, header fields SHOULD NOT be the Internet. However, for the purposes of this standard, header
reordered when a message is transported or transformed. More fields SHOULD NOT be reordered when a message is transported or
importantly, the trace header fields and resent header fields MUST NOT transformed. More importantly, the trace header fields and resent
be reordered, and SHOULD be kept in blocks prepended to the message. See header fields MUST NOT be reordered, and SHOULD be kept in blocks
sections 3.6.6 and 3.6.7 for more information. prepended to the message. See sections 3.6.6 and 3.6.7 for more
information.
The only required header fields are the origination date field and the The only required header fields are the origination date field and
originator address field(s). All other header fields are syntactically the originator address field(s). All other header fields are
optional. More information is contained in the table following this syntactically optional. More information is contained in the table
definition. following this definition.
fields = *(trace fields = *(trace
*(resent-date / *(resent-date /
resent-from / resent-from /
resent-sender / resent-sender /
resent-to / resent-to /
resent-cc / resent-cc /
resent-bcc / resent-bcc /
resent-msg-id)) resent-msg-id))
*(orig-date / *(orig-date /
skipping to change at line 768 skipping to change at page 19, line 15
cc / cc /
bcc / bcc /
message-id / message-id /
in-reply-to / in-reply-to /
references / references /
subject / subject /
comments / comments /
keywords / keywords /
optional-field) optional-field)
The following table indicates limits on the number of times each field The following table indicates limits on the number of times each
may occur in a message header as well as any special limitations on the field may occur in a message header as well as any special
use of those fields. An asterisk next to a value in the minimum or limitations on the use of those fields. An asterisk next to a value
maximum column indicates that a special restriction appears in the Notes in the minimum or maximum column indicates that a special restriction
column. appears in the Notes column.
Field Min number Max number Notes Field Min number Max number Notes
trace 0 unlimited Block prepended - see trace 0 unlimited Block prepended - see
3.6.7 3.6.7
resent-date 0* unlimited* One per block, required resent-date 0* unlimited* One per block, required
if other resent fields if other resent fields
present - see 3.6.6 present - see 3.6.6
resent-from 0 unlimited* One per block - see resent-from 0 unlimited* One per block - see
3.6.6 3.6.6
resent-sender 0* unlimited* One per block, MUST resent-sender 0* unlimited* One per block, MUST
occur with multi-address occur with multi-address
resent-from - see 3.6.6 resent-from - see 3.6.6
resent-to 0 unlimited* One per block - see resent-to 0 unlimited* One per block - see
3.6.6 3.6.6
resent-cc 0 unlimited* One per block - see resent-cc 0 unlimited* One per block - see
3.6.6 3.6.6
resent-bcc 0 unlimited* One per block - see resent-bcc 0 unlimited* One per block - see
3.6.6 3.6.6
skipping to change at line 834 skipping to change at page 20, line 32
replies - see 3.6.4 replies - see 3.6.4
subject 0 1 subject 0 1
comments 0 unlimited comments 0 unlimited
keywords 0 unlimited keywords 0 unlimited
optional-field 0 unlimited optional-field 0 unlimited
The exact interpretation of each field is described in subsequent The exact interpretation of each field is described in subsequent
sections. sections.
3.6.1. The origination date field 3.6.1. The origination date field
The origination date field consists of the field name "Date" followed by The origination date field consists of the field name "Date" followed
a date-time specification. by a date-time specification.
orig-date = "Date:" date-time CRLF orig-date = "Date:" date-time CRLF
The origination date specifies the date and time at which the creator of The origination date specifies the date and time at which the creator
the message indicated that the message was complete and ready to enter of the message indicated that the message was complete and ready to
the mail delivery system. For instance, this might be the time that a enter the mail delivery system. For instance, this might be the time
user pushes the "send" or "submit" button in an application program. In that a user pushes the "send" or "submit" button in an application
any case, it is specifically not intended to convey the time that the program. In any case, it is specifically not intended to convey the
message is actually transported, but rather the time at which the human time that the message is actually transported, but rather the time at
or other creator of the message has put the message into its final form, which the human or other creator of the message has put the message
ready for transport. (For example, a portable computer user who is not into its final form, ready for transport. (For example, a portable
connected to a network might queue a message for delivery. The computer user who is not connected to a network might queue a message
origination date is intended to contain the date and time that the user for delivery. The origination date is intended to contain the date
queued the message, not the time when the user connected to the network and time that the user queued the message, not the time when the user
to send the message.) connected to the network to send the message.)
3.6.2. Originator fields 3.6.2. Originator fields
The originator fields of a message consist of the from field, the sender The originator fields of a message consist of the from field, the
field (when applicable) and optionally the reply-to field. The from sender field (when applicable), and optionally the reply-to field.
field consists of the field name "From" and a comma-separated list of The from field consists of the field name "From" and a
one or more mailbox specifications. If the from field contains more than comma-separated list of one or more mailbox specifications. If the
one mailbox specification in the mailbox-list, then the sender field, from field contains more than one mailbox specification in the
containing the field name "Sender" and a single mailbox specification, mailbox-list, then the sender field, containing the field name
MUST appear in the message. In either case, an optional reply-to field "Sender" and a single mailbox specification, MUST appear in the
MAY also be included, which contains the field name "Reply-To" and a message. In either case, an optional reply-to field MAY also be
comma-separated list of one or more addresses. included, which contains the field name "Reply-To" and a
comma-separated list of one or more addresses.
from = "From:" mailbox-list CRLF from = "From:" mailbox-list CRLF
sender = "Sender:" mailbox CRLF sender = "Sender:" mailbox CRLF
reply-to = "Reply-To:" address-list CRLF reply-to = "Reply-To:" address-list CRLF
The originator fields indicate the mailbox(es) of the source of the The originator fields indicate the mailbox(es) of the source of the
message. The "From:" field specifies the author(s) of the message, that message. The "From:" field specifies the author(s) of the message,
is, the mailbox(es) of the person(s) or system(s) responsible for the that is, the mailbox(es) of the person(s) or system(s) responsible
writing of the message. The "Sender:" field specifies the mailbox of the for the writing of the message. The "Sender:" field specifies the
agent responsible for the actual transmission of the message. For mailbox of the agent responsible for the actual transmission of the
example, if a secretary were to send a message for another person, the message. For example, if a secretary were to send a message for
mailbox of the secretary would appear in the "Sender:" field and the another person, the mailbox of the secretary would appear in the
mailbox of the actual author would appear in the "From:" field. If the "Sender:" field and the mailbox of the actual author would appear in
originator of the message can be indicated by a single mailbox and the the "From:" field. If the originator of the message can be indicated
author and transmitter are identical, the "Sender:" field SHOULD NOT be by a single mailbox and the author and transmitter are identical, the
used. Otherwise, both fields SHOULD appear. "Sender:" field SHOULD NOT be used. Otherwise, both fields SHOULD
appear.
The originator fields also provide the information required when The originator fields also provide the information required when
replying to a message. When the "Reply-To:" field is present, it replying to a message. When the "Reply-To:" field is present, it
indicates the mailbox(es) to which the author of the message suggests indicates the mailbox(es) to which the author of the message suggests
that replies be sent. In the absence of the "Reply-To:" field, replies that replies be sent. In the absence of the "Reply-To:" field,
SHOULD by default be sent to the mailbox(es) specified in the "From:" replies SHOULD by default be sent to the mailbox(es) specified in the
field unless otherwise specified by the person composing the reply. "From:" field unless otherwise specified by the person composing the
reply.
In all cases, the "From:" field SHOULD NOT contain any mailbox that does In all cases, the "From:" field SHOULD NOT contain any mailbox that
not belong to the author(s) of the message. See also section 3.6.3 for does not belong to the author(s) of the message. See also section
more information on forming the destination addresses for a reply. 3.6.3 for more information on forming the destination addresses for a
reply.
3.6.3. Destination address fields 3.6.3. Destination address fields
The destination fields of a message consist of three possible fields, The destination fields of a message consist of three possible fields,
each of the same form: The field name, which is either "To", "Cc", or each of the same form: The field name, which is either "To", "Cc", or
"Bcc", followed by a comma-separated list of one or more addresses "Bcc", followed by a comma-separated list of one or more addresses
(either mailbox or group syntax). (either mailbox or group syntax).
to = "To:" address-list CRLF to = "To:" address-list CRLF
cc = "Cc:" address-list CRLF cc = "Cc:" address-list CRLF
bcc = "Bcc:" (address-list / [CFWS]) CRLF bcc = "Bcc:" (address-list / [CFWS]) CRLF
The destination fields specify the recipients of the message. Each The destination fields specify the recipients of the message. Each
destination field may have one or more addresses, and each of the destination field may have one or more addresses, and each of the
addresses indicate the intended recipients of the message. The only addresses indicate the intended recipients of the message. The only
difference between the three fields is how each is used. difference between the three fields is how each is used.
The "To:" field contains the address(es) of the primary recipient(s) of The "To:" field contains the address(es) of the primary recipient(s)
the message. of the message.
The "Cc:" field (where the "Cc" means "Carbon Copy" in the sense of The "Cc:" field (where the "Cc" means "Carbon Copy" in the sense of
making a copy on a typewriter using carbon paper) contains the addresses making a copy on a typewriter using carbon paper) contains the
of others who are to receive the message, though the content of the addresses of others who are to receive the message, though the
message may not be directed at them. content of the message may not be directed at them.
The "Bcc:" field (where the "Bcc" means "Blind Carbon Copy") contains The "Bcc:" field (where the "Bcc" means "Blind Carbon Copy") contains
addresses of recipients of the message whose addresses are not to be addresses of recipients of the message whose addresses are not to be
revealed to other recipients of the message. There are three ways in revealed to other recipients of the message. There are three ways in
which the "Bcc:" field is used. In the first case, when a message which the "Bcc:" field is used. In the first case, when a message
containing a "Bcc:" field is prepared to be sent, the "Bcc:" line is containing a "Bcc:" field is prepared to be sent, the "Bcc:" line is
removed even though all of the recipients (including those specified in removed even though all of the recipients (including those specified
the "Bcc:" field) are sent a copy of the message. In the second case, in the "Bcc:" field) are sent a copy of the message. In the second
recipients specified in the "To:" and "Cc:" lines each are sent a copy case, recipients specified in the "To:" and "Cc:" lines each are sent
of the message with the "Bcc:" line removed as above, but the recipients a copy of the message with the "Bcc:" line removed as above, but the
on the "Bcc:" line get a separate copy of the message containing a recipients on the "Bcc:" line get a separate copy of the message
"Bcc:" line. (When there are multiple recipient addresses in the "Bcc:" containing a "Bcc:" line. (When there are multiple recipient
field, some implementations actually send a separate copy of the message addresses in the "Bcc:" field, some implementations actually send a
to each recipient with a "Bcc:" containing only the address of that separate copy of the message to each recipient with a "Bcc:"
particular recipient.) Finally, since a "Bcc:" field may contain no containing only the address of that particular recipient.) Finally,
addresses, a "Bcc:" field can be sent without any addresses indicating since a "Bcc:" field may contain no addresses, a "Bcc:" field can be
to the recipients that blind copies were sent to someone. Which method sent without any addresses indicating to the recipients that blind
to use with "Bcc:" fields is implementation dependent, but refer to the copies were sent to someone. Which method to use with "Bcc:" fields
"Security Considerations" section of this document for a discussion of is implementation dependent, but refer to the "Security
each. Considerations" section of this document for a discussion of each.
When a message is a reply to another message, the mailboxes of the When a message is a reply to another message, the mailboxes of the
authors of the original message (the mailboxes in the "From:" field) or authors of the original message (the mailboxes in the "From:" field)
mailboxes specified in the "Reply-To:" field (if it exists) MAY appear or mailboxes specified in the "Reply-To:" field (if it exists) MAY
in the "To:" field of the reply, since these would normally be the appear in the "To:" field of the reply since these would normally be
primary recipients of the reply. If a reply is sent to a message that the primary recipients of the reply. If a reply is sent to a message
has destination fields, it is often desirable to send a copy of the that has destination fields, it is often desirable to send a copy of
reply to all of the recipients of the message, in addition to the the reply to all of the recipients of the message, in addition to the
author. When such a reply is formed, addresses in the "To:" and "Cc:" author. When such a reply is formed, addresses in the "To:" and
fields of the original message MAY appear in the "Cc:" field of the "Cc:" fields of the original message MAY appear in the "Cc:" field of
reply, since these are normally secondary recipients of the reply. If a the reply, since these are normally secondary recipients of the
"Bcc:" field is present in the original message, addresses in that field reply. If a "Bcc:" field is present in the original message,
MAY appear in the "Bcc:" field of the reply, but SHOULD NOT appear in addresses in that field MAY appear in the "Bcc:" field of the reply,
the "To:" or "Cc:" fields. but SHOULD NOT appear in the "To:" or "Cc:" fields.
Note: Some mail applications have automatic reply commands that include Note: Some mail applications have automatic reply commands that
the destination addresses of the original message in the destination include the destination addresses of the original message in the
addresses of the reply. How those reply commands behave is destination addresses of the reply. How those reply commands behave
implementation dependent and is beyond the scope of this document. In is implementation dependent and is beyond the scope of this document.
particular, whether or not to include the original destination addresses In particular, whether or not to include the original destination
when the original message had a "Reply-To:" field is not addressed here. addresses when the original message had a "Reply-To:" field is not
addressed here.
3.6.4. Identification fields 3.6.4. Identification fields
Though optional, every message SHOULD have a "Message-ID:" field. Though optional, every message SHOULD have a "Message-ID:" field.
Furthermore, reply messages SHOULD have "In-Reply-To:" and "References:" Furthermore, reply messages SHOULD have "In-Reply-To:" and
fields as appropriate, as described below. "References:" fields as appropriate, as described below.
The "Message-ID:" field contains a single unique message identifier. The The "Message-ID:" field contains a single unique message identifier.
"References:" and "In-Reply-To:" field each contain one or more unique The "References:" and "In-Reply-To:" field each contain one or more
message identifiers, optionally separated by CFWS. unique message identifiers, optionally separated by CFWS.
The message identifier (msg-id) is similar in syntax to an addr-spec The message identifier (msg-id) is similar in syntax to an angle-addr
construct enclosed in the angle bracket characters, "<" and ">", without construct without the internal CFWS.
the internal CFWS.
message-id = "Message-ID:" msg-id CRLF message-id = "Message-ID:" msg-id CRLF
in-reply-to = "In-Reply-To:" 1*msg-id CRLF in-reply-to = "In-Reply-To:" 1*msg-id CRLF
references = "References:" 1*msg-id CRLF references = "References:" 1*msg-id CRLF
msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS] msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS]
id-left = dot-atom-text / no-fold-quote / obs-id-left id-left = dot-atom-text / no-fold-quote / obs-id-left
skipping to change at line 992 skipping to change at page 24, line 4
references = "References:" 1*msg-id CRLF references = "References:" 1*msg-id CRLF
msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS] msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS]
id-left = dot-atom-text / no-fold-quote / obs-id-left id-left = dot-atom-text / no-fold-quote / obs-id-left
id-right = dot-atom-text / no-fold-literal / obs-id-right id-right = dot-atom-text / no-fold-literal / obs-id-right
no-fold-quote = DQUOTE *(qtext / quoted-pair) DQUOTE no-fold-quote = DQUOTE *(qtext / quoted-pair) DQUOTE
no-fold-literal = "[" *(dtext / quoted-pair) "]" no-fold-literal = "[" *(dtext / quoted-pair) "]"
The "Message-ID:" field provides a unique message identifier that refers The "Message-ID:" field provides a unique message identifier that
to a particular version of a particular message. The uniqueness of the refers to a particular version of a particular message. The
message identifier is guaranteed by the host that generates it (see uniqueness of the message identifier is guaranteed by the host that
below). This message identifier is intended to be machine readable and generates it (see below). This message identifier is intended to be
not necessarily meaningful to humans. A message identifier pertains to machine readable and not necessarily meaningful to humans. A message
exactly one instantiation of a particular message; subsequent revisions identifier pertains to exactly one instantiation of a particular
to the message each receive new message identifiers. message; subsequent revisions to the message each receive new message
identifiers.
Note: There are many instances when messages are "changed", but those Note: There are many instances when messages are "changed", but those
changes do not constitute a new instantiation of that message, and changes do not constitute a new instantiation of that message, and
therefore the message would not get a new message identifier. For therefore the message would not get a new message identifier. For
example, when messages are introduced into the transport system, they example, when messages are introduced into the transport system, they
are often prepended with additional header fields such as trace fields are often prepended with additional header fields such as trace
(described in section 3.6.7) and resent fields (described in section fields (described in section 3.6.7) and resent fields (described in
3.6.6). The addition of such header fields does not change the identity section 3.6.6). The addition of such header fields does not change
of the message and therefore the original "Message-ID:" field is the identity of the message and therefore the original "Message-ID:"
retained. In all cases, it is the meaning that the sender of the message field is retained. In all cases, it is the meaning that the sender
wishes to convey (i.e., whether this is the same message or a different of the message wishes to convey (i.e., whether this is the same
message) that determines whether or not the "Message-ID:" field changes, message or a different message) that determines whether or not the
not any particular syntactic difference that appears (or does not "Message-ID:" field changes, not any particular syntactic difference
appear) in the message. that appears (or does not appear) in the message.
The "In-Reply-To:" and "References:" fields are used when creating a The "In-Reply-To:" and "References:" fields are used when creating a
reply to a message. They hold the message identifier of the original reply to a message. They hold the message identifier of the original
message and the message identifiers of other messages (for example, in message and the message identifiers of other messages (for example,
the case of a reply to a message which was itself a reply). The "In- in the case of a reply to a message which was itself a reply). The
Reply-To:" field may be used to identify the message (or messages) to "In-Reply-To:" field may be used to identify the message (or
which the new message is a reply, while the "References:" field may be messages) to which the new message is a reply, while the
used to identify a "thread" of conversation. "References:" field may be used to identify a "thread" of
conversation.
When creating a reply to a message, the "In-Reply-To:" and "References:" When creating a reply to a message, the "In-Reply-To:" and
fields of the resultant message are constructed as follows: "References:" fields of the resultant message are constructed as
follows:
The "In-Reply-To:" field will contain the contents of the "Message-ID:" The "In-Reply-To:" field will contain the contents of the "Message-
field of the message to which this one is a reply (the "parent ID:" field of the message to which this one is a reply (the "parent
message"). If there is more than one parent message, then the "In-Reply- message"). If there is more than one parent message, then the "In-
To:" field will contain the contents of all of the parents' "Message- Reply-To:" field will contain the contents of all of the parents'
ID:" fields. If there is no "Message-ID:" field in any of the parent "Message-ID:" fields. If there is no "Message-ID:" field in any of
messages, then the new message will have no "In-Reply-To:" field. the parent messages, then the new message will have no "In-Reply-To:"
field.
The "References:" field will contain the contents of the parent's The "References:" field will contain the contents of the parent's
"References:" field (if any) followed by the contents of the parent's "References:" field (if any) followed by the contents of the parent's
"Message-ID:" field (if any). If the parent message does not contain a "Message-ID:" field (if any). If the parent message does not contain
"References:" field but does have an "In-Reply-To:" field containing a a "References:" field but does have an "In-Reply-To:" field
single message identifier, then the "References:" field will contain the containing a single message identifier, then the "References:" field
contents of the parent's "In-Reply-To:" field followed by the contents will contain the contents of the parent's "In-Reply-To:" field
of the parent's "Message-ID:" field (if any). If the parent has none of followed by the contents of the parent's "Message-ID:" field (if
the "References:", "In-Reply-To:", or "Message-ID:" fields, then the new any). If the parent has none of the "References:", "In-Reply-To:",
message will have no "References:" field. or "Message-ID:" fields, then the new message will have no
"References:" field.
Note: Some implementations parse the "References:" field to display the Note: Some implementations parse the "References:" field to display
"thread of the discussion". These implementations assume that each new the "thread of the discussion". These implementations assume that
message is a reply to a single parent and hence that they can walk each new message is a reply to a single parent and hence that they
backwards through the "References:" field to find the parent of each can walk backwards through the "References:" field to find the parent
message listed there. Therefore, trying to form a "References:" field of each message listed there. Therefore, trying to form a
for a reply that has multiple parents is discouraged. "References:" field for a reply that has multiple parents is
discouraged and how to do so is not defined in this document.
The message identifier (msg-id) itself MUST be a globally unique The message identifier (msg-id) itself MUST be a globally unique
identifier for a message. The generator of the message identifier MUST identifier for a message. The generator of the message identifier
guarantee that the msg-id is unique. There are several algorithms that MUST guarantee that the msg-id is unique. There are several
can be used to accomplish this. Since the msg-id has an similar syntax algorithms that can be used to accomplish this. Since the msg-id has
to addr-spec (identical except that comments and folding white space are a similar syntax to angle-addr (identical except that comments and
not allowed), a good method is to put the domain name (or a domain folding white space are not allowed), a good method is to put the
literal IP address) of the host on which the message identifier was domain name (or a domain literal IP address) of the host on which the
created on the right hand side of the "@", and put a combination of the message identifier was created on the right hand side of the "@", and
current absolute date and time along with some other currently unique put a combination of the current absolute date and time along with
(perhaps sequential) identifier available on the system (for example, a some other currently unique (perhaps sequential) identifier available
process id number) on the left hand side. Using a date on the left hand on the system (for example, a process id number) on the left hand
side and a domain name or domain literal on the right hand side makes it side. Using a date on the left hand side and a domain name or domain
possible to guarantee uniqueness since no two hosts use the same domain literal on the right hand side makes it possible to guarantee
name or IP address at the same time. Though other algorithms will work, uniqueness since no two hosts use the same domain name or IP address
it is RECOMMENDED that the right hand side contain some domain at the same time. Though other algorithms will work, it is
identifier (either of the host itself or otherwise) such that the RECOMMENDED that the right hand side contain some domain identifier
generator of the message identifier can guarantee the uniqueness of the (either of the host itself or otherwise) such that the generator of
left hand side within the scope of that domain. the message identifier can guarantee the uniqueness of the left hand
side within the scope of that domain.
Semantically, the angle bracket characters are not part of the msg-id; Semantically, the angle bracket characters are not part of the
the msg-id is what is contained between the two angle bracket msg-id; the msg-id is what is contained between the two angle bracket
characters. characters.
3.6.5. Informational fields 3.6.5. Informational fields
The informational fields are all optional. The "Keywords:" field The informational fields are all optional. The "Keywords:" field
contains a comma-separated list of one or more words or quoted-strings. contains a comma-separated list of one or more words or
The "Subject:" and "Comments:" fields are unstructured fields as defined quoted-strings. The "Subject:" and "Comments:" fields are
in section 2.2.1, and therefore may contain text or folding white space. unstructured fields as defined in section 2.2.1, and therefore may
contain text or folding white space.
subject = "Subject:" unstructured CRLF subject = "Subject:" unstructured CRLF
comments = "Comments:" unstructured CRLF comments = "Comments:" unstructured CRLF
keywords = "Keywords:" phrase *("," phrase) CRLF keywords = "Keywords:" phrase *("," phrase) CRLF
These three fields are intended to have only human-readable content with These three fields are intended to have only human-readable content
information about the message. The "Subject:" field is the most common with information about the message. The "Subject:" field is the most
and contains a short string identifying the topic of the message. When common and contains a short string identifying the topic of the
used in a reply, the field body MAY start with the string "Re: " (from message. When used in a reply, the field body MAY start with the
the Latin "res", in the matter of) followed by the contents of the string "Re: " (from the Latin "res", in the matter of) followed by
"Subject:" field body of the original message. If this is done, only one the contents of the "Subject:" field body of the original message.
instance of the literal string "Re: " ought to be used since use of If this is done, only one instance of the literal string "Re: " ought
other strings or more than one instance can lead to undesirable to be used since use of other strings or more than one instance can
consequences. The "Comments:" field contains any additional comments on lead to undesirable consequences. The "Comments:" field contains any
the text of the body of the message. The "Keywords:" field contains a additional comments on the text of the body of the message. The
comma-separated list of important words and phrases that might be useful "Keywords:" field contains a comma-separated list of important words
for the recipient. and phrases that might be useful for the recipient.
3.6.6. Resent fields 3.6.6. Resent fields
Resent fields SHOULD be added to any message that is reintroduced by a Resent fields SHOULD be added to any message that is reintroduced by
user into the transport system. A separate set of resent fields SHOULD a user into the transport system. A separate set of resent fields
be added each time this is done. All of the resent fields corresponding SHOULD be added each time this is done. All of the resent fields
to a particular resending of the message SHOULD be together. Each new corresponding to a particular resending of the message SHOULD be
set of resent fields is prepended to the message; that is, the most together. Each new set of resent fields is prepended to the message;
recent set of resent fields appear earlier in the message. No other that is, the most recent set of resent fields appear earlier in the
fields in the message are changed when resent fields are added. message. No other fields in the message are changed when resent
fields are added.
Each of the resent fields corresponds to a particular field elsewhere in Each of the resent fields corresponds to a particular field elsewhere
the syntax. For instance, the "Resent-Date:" field corresponds to the in the syntax. For instance, the "Resent-Date:" field corresponds to
"Date:" field and the "Resent-To:" field corresponds to the "To:" field. the "Date:" field and the "Resent-To:" field corresponds to the "To:"
In each case, the syntax for the field body is identical to the syntax field. In each case, the syntax for the field body is identical to
given previously for the corresponding field. the syntax given previously for the corresponding field.
When resent fields are used, the "Resent-From:" and "Resent-Date:" When resent fields are used, the "Resent-From:" and "Resent-Date:"
fields MUST be sent. The "Resent-Message-ID:" field SHOULD be sent. fields MUST be sent. The "Resent-Message-ID:" field SHOULD be sent.
"Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be "Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be
identical to "Resent-From:". identical to "Resent-From:".
resent-date = "Resent-Date:" date-time CRLF resent-date = "Resent-Date:" date-time CRLF
resent-from = "Resent-From:" mailbox-list CRLF resent-from = "Resent-From:" mailbox-list CRLF
resent-sender = "Resent-Sender:" mailbox CRLF resent-sender = "Resent-Sender:" mailbox CRLF
resent-to = "Resent-To:" address-list CRLF resent-to = "Resent-To:" address-list CRLF
resent-cc = "Resent-Cc:" address-list CRLF resent-cc = "Resent-Cc:" address-list CRLF
resent-bcc = "Resent-Bcc:" (address-list / [CFWS]) CRLF resent-bcc = "Resent-Bcc:" (address-list / [CFWS]) CRLF
resent-msg-id = "Resent-Message-ID:" msg-id CRLF resent-msg-id = "Resent-Message-ID:" msg-id CRLF
Resent fields are used to identify a message as having been reintroduced Resent fields are used to identify a message as having been
into the transport system by a user. The purpose of using resent fields reintroduced into the transport system by a user. The purpose of
is to have the message appear to the final recipient as if it were sent using resent fields is to have the message appear to the final
directly by the original sender, with all of the original fields recipient as if it were sent directly by the original sender, with
remaining the same. Each set of resent fields correspond to a particular all of the original fields remaining the same. Each set of resent
resending event. That is, if a message is resent multiple times, each fields correspond to a particular resending event. That is, if a
set of resent fields gives identifying information for each individual message is resent multiple times, each set of resent fields gives
time. Resent fields are strictly informational. They MUST NOT be used in identifying information for each individual time. Resent fields are
the normal processing of replies or other such automatic actions on strictly informational. They MUST NOT be used in the normal
messages. processing of replies or other such automatic actions on messages.
Note: Reintroducing a message into the transport system and using resent Note: Reintroducing a message into the transport system and using
fields is a different operation from "forwarding". Forwarding has two resent fields is a different operation from "forwarding".
meanings: First, there is a sense of forwarding in that a mail reading "Forwarding" has two meanings: One sense of forwarding is that a mail
program can be told by the user to forward a copy of the message to reading program can be told by a user to forward a copy of a message
another person is to make a message the body of a new message. A to another person, making the forwarded message the body of the new
forwarded message in this sense does not appear to have come from the message. A forwarded message in this sense does not appear to have
original sender, but is an entirely new message from the forwarder of come from the original sender, but is an entirely new message from
the message. Second, forwarding is also used to mean when a mail the forwarder of the message. On the other hand, forwarding is also
transport program gets a message and forwards it on to a different used to mean when a mail transport program gets a message and
destination for final delivery. Resent header fields are not intended forwards it on to a different destination for final delivery. Resent
for use with either type of forwarding. header fields are not intended for use with either type of
forwarding.
The resent originator fields indicate the mailbox of the person(s) or The resent originator fields indicate the mailbox of the person(s) or
system(s) that resent the message. As with the regular originator system(s) that resent the message. As with the regular originator
fields, there are two forms: a simple "Resent-From:" form which contains fields, there are two forms: a simple "Resent-From:" form which
the mailbox of the individual doing the resending, and the more complex contains the mailbox of the individual doing the resending, and the
form, when one individual (identified in the "Resent-Sender:" field) more complex form, when one individual (identified in the
resends a message on behalf of one or more others (identified in the "Resent-Sender:" field) resends a message on behalf of one or more
"Resent-From:" field). others (identified in the "Resent-From:" field).
Note: When replying to a resent message, replies behave just as they Note: When replying to a resent message, replies behave just as they
would with any other message, using the original "From:", "Reply-To:", would with any other message, using the original "From:",
"Message-ID:", and other fields. The resent fields are only "Reply-To:", "Message-ID:", and other fields. The resent fields are
informational and MUST NOT be used in the normal processing of replies. only informational and MUST NOT be used in the normal processing of
replies.
The "Resent-Date:" indicates the date and time at which the resent The "Resent-Date:" indicates the date and time at which the resent
message is dispatched by the resender of the message. Like the "Date:" message is dispatched by the resender of the message. Like the
field, it is not the date and time that the message was actually "Date:" field, it is not the date and time that the message was
transported. actually transported.
The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function
identically to the "To:", "Cc:", and "Bcc:" fields respectively, except identically to the "To:", "Cc:", and "Bcc:" fields respectively,
that they indicate the recipients of the resent message, not the except that they indicate the recipients of the resent message, not
recipients of the original message. the recipients of the original message.
The "Resent-Message-ID:" field provides a unique identifier for the The "Resent-Message-ID:" field provides a unique identifier for the
resent message. resent message.
3.6.7. Trace fields 3.6.7. Trace fields
The trace fields are a group of header fields consisting of an optional The trace fields are a group of header fields consisting of an
"Return-Path:" field, and one or more "Received:" fields. The "Return- optional "Return-Path:" field, and one or more "Received:" fields.
Path:" header field contains a pair of angle brackets that enclose an The "Return-Path:" header field contains a pair of angle brackets
optional addr-spec. The "Received:" field contains a (possibly empty) that enclose an optional addr-spec. The "Received:" field contains a
list of name/value pairs followed by a semicolon and a date-time (possibly empty) list of name/value pairs followed by a semicolon and
specification. The first item of the name/value pair is defined by item- a date-time specification. The first item of the name/value pair is
name, and the second item is either an addr-spec, an atom, a domain, or defined by item-name, and the second item is either an addr-spec, an
a msg-id. Further restrictions may be applied to the syntax of the trace atom, a domain, or a msg-id. Further restrictions may be applied to
fields by standards that provide for their use, such as [SMTP]. the syntax of the trace fields by standards that provide for their
use, such as [RFC2821].
trace = [return] trace = [return]
1*received 1*received
return = "Return-Path:" path CRLF return = "Return-Path:" path CRLF
path = ([CFWS] "<" ([CFWS] / addr-spec) ">" [CFWS]) / path = ([CFWS] "<" ([CFWS] / addr-spec) ">" [CFWS]) /
obs-path obs-path
received = "Received:" name-val-list ";" date-time CRLF received = "Received:" name-val-list ";" date-time CRLF
name-val-list = [CFWS] [name-val-pair *(CFWS name-val-pair)] name-val-list = [CFWS] [name-val-pair *(CFWS name-val-pair)]
name-val-pair = item-name CFWS item-value name-val-pair = item-name CFWS item-value
item-name = ALPHA *(["-"] (ALPHA / DIGIT)) item-name = ALPHA *(["-"] (ALPHA / DIGIT))
item-value = addr-spec / atom / domain / msg-id item-value = 1*angle-addr / addr-spec /
atom / domain / msg-id
A full discussion of the Internet mail use of trace fields is contained A full discussion of the Internet mail use of trace fields is
in [SMTP]. For the purposes of this standard, the trace fields are contained in [RFC2821]. For the purposes of this standard, the trace
strictly informational, and any formal interpretation of them is outside fields are strictly informational, and any formal interpretation of
of the scope of this document. them is outside of the scope of this document.
3.6.8. Optional fields 3.6.8. Optional fields
Fields may appear in messages that are otherwise unspecified in this Fields may appear in messages that are otherwise unspecified in this
standard. They MUST conform to the syntax of an optional-field. This is standard. They MUST conform to the syntax of an optional-field.
a field name, made up of the printable US-ASCII characters except SP and This is a field name, made up of the printable US-ASCII characters
colon, followed by a colon, followed by any text which conforms to except SP and colon, followed by a colon, followed by any text which
unstructured. conforms to unstructured.
The field names of any optional-field MUST NOT be identical to any field The field names of any optional-field MUST NOT be identical to any
name specified elsewhere in this standard. field name specified elsewhere in this standard.
optional-field = field-name ":" unstructured CRLF optional-field = field-name ":" unstructured CRLF
field-name = 1*ftext field-name = 1*ftext
ftext = %d33-57 / ; Any character except ftext = %d33-57 / ; Any character except
%d59-126 ; controls, SP, and %d59-126 ; controls, SP, and
; ":". ; ":".
For the purposes of this standard, any optional field is uninterpreted. For the purposes of this standard, any optional field is
uninterpreted.
4. Obsolete Syntax 4. Obsolete Syntax
Earlier versions of this standard allowed for different (usually more Earlier versions of this standard allowed for different (usually more
liberal) syntax than is allowed in this version. Also, there have been liberal) syntax than is allowed in this version. Also, there have
syntactic elements used in messages on the Internet whose interpretation been syntactic elements used in messages on the Internet whose
have never been documented. Though some of these syntactic forms MUST interpretation have never been documented. Though some of these
NOT be generated according to the grammar in section 3, they MUST be syntactic forms MUST NOT be generated according to the grammar in
accepted and parsed by a conformant receiver. This section documents section 3, they MUST be accepted and parsed by a conformant receiver.
many of these syntactic elements. Taking the grammar in section 3 and This section documents many of these syntactic elements. Taking the
adding the definitions presented in this section will result in the grammar in section 3 and adding the definitions presented in this
grammar to use for interpretation of messages. section will result in the grammar to use for interpretation of
messages.
Note: This section identifies syntactic forms that any implementation Note: This section identifies syntactic forms that any implementation
MUST reasonably interpret. However, there are certainly Internet MUST reasonably interpret. However, there are certainly Internet
messages which do not conform to even the additional syntax given in messages which do not conform to even the additional syntax given in
this section. The fact that a particular form does not appear in any this section. The fact that a particular form does not appear in any
section of this document is not justification for computer programs to section of this document is not justification for computer programs
crash or for malformed data to be irretrievably lost by any to crash or for malformed data to be irretrievably lost by any
implementation. To repeat an example, though this document requires implementation. To repeat an example, though this document requires
lines in messages to be no longer than 998 characters, silently lines in messages to be no longer than 998 characters, silently
discarding the 999th and subsequent characters in a line without warning discarding the 999th and subsequent characters in a line without
would still be bad behavior for an implementation. It is up to the warning would still be bad behavior for an implementation. It is up
implementation to deal with messages robustly. to the implementation to deal with messages robustly.
One important difference between the obsolete (interpreting) and the One important difference between the obsolete (interpreting) and the
current (generating) syntax is that in structured header field bodies current (generating) syntax is that in structured header field bodies
(i.e., between the colon and the CRLF of any structured header field), (i.e., between the colon and the CRLF of any structured header
white space characters, including folding white space, and comments field), white space characters, including folding white space, and
could be freely inserted between any syntactic tokens. This allowed many comments can be freely inserted between any syntactic tokens. This
complex forms that have proven difficult for some implementations to allows many complex forms that have proven difficult for some
parse. implementations to parse.
Another key difference between the obsolete and the current syntax is Another key difference between the obsolete and the current syntax is
that the rule in section 3.2.3 regarding lines composed entirely of that the rule in section 3.2.3 regarding lines composed entirely of
white space in comments and folding white space does not apply. See the white space in comments and folding white space does not apply. See
discussion of folding white space in section 4.2 below. the discussion of folding white space in section 4.2 below.
Finally, certain characters that were formerly allowed in messages Finally, certain characters that were formerly allowed in messages
appear in this section. The NUL character (ASCII value 0) was once appear in this section. The NUL character (ASCII value 0) was once
allowed, but is no longer for compatibility reasons. CR and LF were allowed, but is no longer for compatibility reasons. CR and LF were
allowed to appear in messages other than as CRLF; this use is also shown allowed to appear in messages other than as CRLF; this use is also
here. shown here.
Other differences in syntax and semantics are noted in the following Other differences in syntax and semantics are noted in the following
sections. sections.
4.1. Miscellaneous obsolete tokens 4.1. Miscellaneous obsolete tokens
These syntactic elements are used elsewhere in the obsolete syntax or in These syntactic elements are used elsewhere in the obsolete syntax or
the main syntax. The obs-char and obs-qp elements each add ASCII value in the main syntax. The obs-char and obs-qp elements each add ASCII
0. Bare CR and bare LF are added to obs-text and obs-utext. The period value 0. Bare CR and bare LF are added to obs-text and obs-utext.
character is added to obs-phrase. The period character is added to obs-phrase. The obs-phrase-list
provides for "empty" elements in a comma-separated list of phrases.
Note: The "period" (or "full stop") character (".") in obs-phrase is not Note: The "period" (or "full stop") character (".") in obs-phrase is
a form that was allowed in earlier versions of this or any other not a form that was allowed in earlier versions of this or any other
standard. Period (nor any other character from specials) was not allowed standard. Period (nor any other character from specials) was not
in phrase because it introduced a parsing difficulty distinguishing allowed in phrase because it introduced a parsing difficulty
between phrases and portions of an addr-spec (see section 4.4). It distinguishing between phrases and portions of an addr-spec (see
appears here because the period character is currently used in many section 4.4). It appears here because the period character is
messages in the display-name portion of addresses, especially for currently used in many messages in the display-name portion of
initials in names, and therefore must be interpreted properly. In the addresses, especially for initials in names, and therefore must be
future, period may appear in the regular syntax of phrase. interpreted properly. In the future, period may appear in the
regular syntax of phrase.
obs-qp = "\" (%d0-127) obs-qp = "\" (%d0-127)
obs-text = *LF *CR *(obs-char *LF *CR) obs-text = *LF *CR *(obs-char *LF *CR)
obs-char = %d0-9 / %d11 / ; %d0-127 except CR and obs-char = %d0-9 / %d11 / ; %d0-127 except CR and
%d12 / %d14-127 ; LF %d12 / %d14-127 ; LF
obs-utext = obs-text obs-utext = obs-text
obs-phrase = word *(word / "." / CFWS) obs-phrase = word *(word / "." / CFWS)
Bare CR and bare LF appear in messages with two different meanings. In obs-phrase-list = phrase / 1*([phrase] [CFWS] "," [CFWS]) [phrase]
many cases, bare CR or bare LF are used improperly instead of CRLF to
indicate line separators. In other case, bare CR and bare LF are used Bare CR and bare LF appear in messages with two different meanings.
simply as ASCII control characters with their traditional ASCII In many cases, bare CR or bare LF are used improperly instead of CRLF
meanings. to indicate line separators. In other cases, bare CR and bare LF are
used simply as ASCII control characters with their traditional ASCII
meanings.
4.2. Obsolete folding white space 4.2. Obsolete folding white space
In the obsolete syntax, any amount of folding white space MAY be In the obsolete syntax, any amount of folding white space MAY be
inserted where the obs-FWS rule is allowed. This creates the possibility inserted where the obs-FWS rule is allowed. This creates the
of having two consecutive "folds" in a line, and therefore the possibility of having two consecutive "folds" in a line, and
possibility that a line which makes up a folded header field could be therefore the possibility that a line which makes up a folded header
composed entirely of white space. field could be composed entirely of white space.
obs-FWS = 1*WSP *(CRLF 1*WSP) obs-FWS = 1*WSP *(CRLF 1*WSP)
4.3. Obsolete Date and Time 4.3. Obsolete Date and Time
The syntax for the obsolete date format allows a 2 digit year in the The syntax for the obsolete date format allows a 2 digit year in the
date field and allows for a list of alphabetic time zone specifications date field and allows for a list of alphabetic time zone
that were used in earlier versions of this standard. It also permits specifications that were used in earlier versions of this standard.
comments and folding white space between many of the tokens. It also permits comments and folding white space between many of the
tokens.
obs-day-of-week = [CFWS] day-name [CFWS] obs-day-of-week = [CFWS] day-name [CFWS]
obs-year = [CFWS] 2*DIGIT [CFWS] obs-year = [CFWS] 2*DIGIT [CFWS]
obs-month = CFWS month-name CFWS obs-month = CFWS month-name CFWS
obs-day = [CFWS] 1*2DIGIT [CFWS] obs-day = [CFWS] 1*2DIGIT [CFWS]
obs-hour = [CFWS] 2DIGIT [CFWS] obs-hour = [CFWS] 2DIGIT [CFWS]
skipping to change at line 1365 skipping to change at page 32, line 16
"EST" / "EDT" / ; Eastern: - 5/ - 4 "EST" / "EDT" / ; Eastern: - 5/ - 4
"CST" / "CDT" / ; Central: - 6/ - 5 "CST" / "CDT" / ; Central: - 6/ - 5
"MST" / "MDT" / ; Mountain: - 7/ - 6 "MST" / "MDT" / ; Mountain: - 7/ - 6
"PST" / "PDT" / ; Pacific: - 8/ - 7 "PST" / "PDT" / ; Pacific: - 8/ - 7
%d65-73 / ; Military zones - "A" %d65-73 / ; Military zones - "A"
%d75-90 / ; through "I" and "K" %d75-90 / ; through "I" and "K"
%d97-105 / ; through "Z", both %d97-105 / ; through "Z", both
%d107-122 ; upper and lower case %d107-122 ; upper and lower case
Where a two or three digit year occurs in a date, the year is to be Where a two or three digit year occurs in a date, the year is to be
interpreted as follows: If a two digit year is encountered whose value interpreted as follows: If a two digit year is encountered whose
is between 00 and 49, the year is interpreted by adding 2000, ending up value is between 00 and 49, the year is interpreted by adding 2000,
with a value between 2000 and 2049. If a two digit year is encountered ending up with a value between 2000 and 2049. If a two digit year is
with a value between 50 and 99, or any three digit year is encountered, encountered with a value between 50 and 99, or any three digit year
the year is interpreted by adding 1900. is encountered, the year is interpreted by adding 1900.
In the obsolete time zone, "UT" and "GMT" are indications of "Universal In the obsolete time zone, "UT" and "GMT" are indications of
Time" and "Greenwich Mean Time" respectively and are both semantically "Universal Time" and "Greenwich Mean Time" respectively and are both
identical to "+0000". semantically identical to "+0000".
The remaining three character zones are the US time zones. The first The remaining three character zones are the US time zones. The first
letter, "E", "C", "M", or "P" stands for "Eastern", "Central", letter, "E", "C", "M", or "P" stands for "Eastern", "Central",
"Mountain" and "Pacific". The second letter is either "S" for "Standard" "Mountain" and "Pacific". The second letter is either "S" for
time, or "D" for "Daylight" (or summer) time. Their interpretations are "Standard" time, or "D" for "Daylight" (or summer) time. Their
as follows: interpretations are as follows:
EDT is semantically equivalent to -0400 EDT is semantically equivalent to -0400
EST is semantically equivalent to -0500 EST is semantically equivalent to -0500
CDT is semantically equivalent to -0500 CDT is semantically equivalent to -0500
CST is semantically equivalent to -0600 CST is semantically equivalent to -0600
MDT is semantically equivalent to -0600 MDT is semantically equivalent to -0600
MST is semantically equivalent to -0700 MST is semantically equivalent to -0700
PDT is semantically equivalent to -0700 PDT is semantically equivalent to -0700
PST is semantically equivalent to -0800 PST is semantically equivalent to -0800
The 1 character military time zones were defined in a non-standard way The 1 character military time zones were defined in a non-standard
in [RFC-822] and are therefore unpredictable in their meaning. The way in [RFC822] and are therefore unpredictable in their meaning.
original definitions of the military zones "A" through "I" are The original definitions of the military zones "A" through "I" are
equivalent to "+0100" through "+0900" respectively; "K", "L", and "M" equivalent to "+0100" through "+0900" respectively; "K", "L", and "M"
are equivalent to "+1000", "+1100", and "+1200" respectively; "N" are equivalent to "+1000", "+1100", and "+1200" respectively; "N"
through "Y" are equivalent to "-0100" through "-1200" respectively; and through "Y" are equivalent to "-0100" through "-1200" respectively;
"Z" is equivalent to "+0000". However, because of the error in [RFC- and "Z" is equivalent to "+0000". However, because of the error in
822], they SHOULD all be considered equivalent to "-0000" unless there [RFC822], they SHOULD all be considered equivalent to "-0000" unless
is out-of-band information confirming their meaning. there is out-of-band information confirming their meaning.
Other multi-character (usually between 3 and 5) alphabetic time zones Other multi-character (usually between 3 and 5) alphabetic time zones
have been used in Internet messages. Any such time zone whose meaning is have been used in Internet messages. Any such time zone whose
not known SHOULD be considered equivalent to "-0000" unless there is meaning is not known SHOULD be considered equivalent to "-0000"
out-of-band information confirming their meaning. unless there is out-of-band information confirming their meaning.
4.4. Obsolete Addressing 4.4. Obsolete Addressing
There are three primary differences in addressing. First, mailbox There are three primary differences in addressing. First, mailbox
addresses were allowed to have a route portion before the addr-spec when addresses were allowed to have a route portion before the addr-spec
enclosed in "<" and ">". The route is simply a comma-separated list of when enclosed in "<" and ">". The route is simply a comma-separated
domain names, each preceded by "@", and the list terminated by a colon. list of domain names, each preceded by "@", and the list terminated
Second, CFWS were allowed between the period-separated elements of by a colon. Second, CFWS were allowed between the period-separated
local-part and domain (i.e., dot-atom was not used). In addition, local- elements of local-part and domain (i.e., dot-atom was not used). In
part is allowed to contain quoted-string in addition to just atom. addition, local-part is allowed to contain quoted-string in addition
Finally, mailbox-list and address-list were allowed to have "null" to just atom. Finally, mailbox-list and address-list were allowed to
members. That is, there could be two or more commas in such a list with have "null" members. That is, there could be two or more commas in
nothing in between them. such a list with nothing in between them.
obs-mailbox = addr-spec / [display-name] obs-route-addr
obs-route-addr = [CFWS] "<" [obs-route] addr-spec ">" [CFWS] obs-angle-addr = [CFWS] "<" [obs-route] addr-spec ">" [CFWS]
obs-route = [CFWS] obs-domain-list ":" [CFWS] obs-route = [CFWS] obs-domain-list ":" [CFWS]
obs-domain-list = "@" domain *(*(CFWS / "," ) [CFWS] "@" domain) obs-domain-list = "@" domain *(*(CFWS / "," ) [CFWS] "@" domain)
obs-local-part = word *("." word) obs-local-part = word *("." word)
obs-domain = atom *("." atom) obs-domain = atom *("." atom)
obs-mbox-list = *([mailbox] [CFWS] "," [CFWS]) obs-mbox-list = 1*([mailbox] [CFWS] "," [CFWS]) [mailbox]
obs-addr-list = *([address] [CFWS] "," [CFWS]) obs-addr-list = 1*([address] [CFWS] "," [CFWS]) [address]
When interpreting addresses, the route portion SHOULD be ignored. When interpreting addresses, the route portion SHOULD be ignored.
4.5. Obsolete header fields 4.5. Obsolete header fields
Syntactically, the primary difference in the obsolete field syntax is Syntactically, the primary difference in the obsolete field syntax is
that it allows multiple occurrences of any of the fields and they may that it allows multiple occurrences of any of the fields and they may
occur in any order. Also, any amount of white space is allowed before occur in any order. Also, any amount of white space is allowed
the ":" at the end of the field name. before the ":" at the end of the field name.
obs-fields = *(obs-return / obs-fields = *(obs-return /
obs-received / obs-received /
obs-orig-date / obs-orig-date /
obs-from / obs-from /
obs-sender / obs-sender /
obs-reply-to / obs-reply-to /
obs-to / obs-to /
obs-cc / obs-cc /
obs-bcc / obs-bcc /
obs-message-id / obs-message-id /
obs-in-reply-to / obs-in-reply-to /
obs-references / obs-references /
obs-subject / obs-subject /
obs-comments / obs-comments /
obs-keywords / obs-keywords /
obs-resent-date /
obs-resent-from / obs-resent-from /
obs-resent-send / obs-resent-send /
obs-resent-rply / obs-resent-rply /
obs-resent-to / obs-resent-to /
obs-resent-cc / obs-resent-cc /
obs-resent-bcc / obs-resent-bcc /
obs-resent-mid / obs-resent-mid /
obs-optional) obs-optional)
Except for destination address fields (described in section 4.5.3), the Except for destination address fields (described in section 4.5.3),
interpretation of multiple occurrences of fields is unspecified. Also, the interpretation of multiple occurrences of fields is unspecified.
the interpretation of trace fields and resent fields which do not occur Also, the interpretation of trace fields and resent fields which do
in blocks prepended to the message is unspecified as well. Unless not occur in blocks prepended to the message is unspecified as well.
otherwise noted in the following sections, interpretation of other Unless otherwise noted in the following sections, interpretation of
fields is identical to the interpretation of their non-obsolete other fields is identical to the interpretation of their non-obsolete
counterparts in section 3. counterparts in section 3.
4.5.1. Obsolete origination date field 4.5.1. Obsolete origination date field
obs-orig-date = "Date" *WSP ":" date-time CRLF obs-orig-date = "Date" *WSP ":" date-time CRLF
4.5.2. Obsolete originator fields 4.5.2. Obsolete originator fields
obs-from = "From" *WSP ":" mailbox-list CRLF obs-from = "From" *WSP ":" mailbox-list CRLF
obs-sender = "Sender" *WSP ":" mailbox CRLF obs-sender = "Sender" *WSP ":" mailbox CRLF
obs-reply-to = "Reply-To" *WSP ":" mailbox-list CRLF obs-reply-to = "Reply-To" *WSP ":" mailbox-list CRLF
4.5.3. Obsolete destination address fields 4.5.3. Obsolete destination address fields
obs-to = "To" *WSP ":" address-list CRLF obs-to = "To" *WSP ":" address-list CRLF
obs-cc = "Cc" *WSP ":" address-list CRLF obs-cc = "Cc" *WSP ":" address-list CRLF
obs-bcc = "Bcc" *WSP ":" (address-list / [CFWS]) CRLF obs-bcc = "Bcc" *WSP ":" (address-list / [CFWS]) CRLF
When multiple occurrences of destination address fields occur in a
When multiple occurrences of destination address fields occur in a message, they SHOULD be treated as if the address-list in the first
message, they SHOULD be treated as if the address-list in the first occurrence of the field is combined with the address lists of the
occurrence of the field is combined with the address lists of the subsequent occurrences by adding a comma and concatenating.
subsequent occurrences by adding a comma and concatenating.
4.5.4. Obsolete identification fields 4.5.4. Obsolete identification fields
The obsolete "In-Reply-To:" and "References:" fields differ from the The obsolete "In-Reply-To:" and "References:" fields differ from the
current syntax in that they allow phrase (words or quoted strings) to current syntax in that they allow phrase (words or quoted strings) to
appear. The obsolete forms of the left and right sides of msg-id allow appear. The obsolete forms of the left and right sides of msg-id
interspersed CFWS, making them syntactically identical to local-part and allow interspersed CFWS, making them syntactically identical to
domain respectively. local-part and domain respectively.
obs-message-id = "Message-ID" *WSP ":" msg-id CRLF obs-message-id = "Message-ID" *WSP ":" msg-id CRLF
obs-in-reply-to = "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF obs-in-reply-to = "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF
obs-references = "References" *WSP ":" *(phrase / msg-id) CRLF obs-references = "References" *WSP ":" *(phrase / msg-id) CRLF
obs-id-left = local-part obs-id-left = local-part
obs-id-right = domain obs-id-right = domain
For purposes of interpretation, the phrases in the "In-Reply-To:" and For purposes of interpretation, the phrases in the "In-Reply-To:" and
"References:" fields are ignored. "References:" fields are ignored.
Semantically, none of the optional CFWS surrounding the local-part and Semantically, none of the optional CFWS surrounding the local-part
the domain are part of the obs-id-left and obs-id-right respectively. and the domain are part of the obs-id-left and obs-id-right
respectively.
4.5.5. Obsolete informational fields 4.5.5. Obsolete informational fields
obs-subject = "Subject" *WSP ":" unstructured CRLF obs-subject = "Subject" *WSP ":" unstructured CRLF
obs-comments = "Comments" *WSP ":" unstructured CRLF obs-comments = "Comments" *WSP ":" unstructured CRLF
obs-keywords = "Keywords" *WSP ":" *([phrase] ",") CRLF obs-keywords = "Keywords" *WSP ":" obs-phrase-list CRLF
4.5.6. Obsolete resent fields 4.5.6. Obsolete resent fields
The obsolete syntax adds a "Resent-Reply-To:" field, which consists of The obsolete syntax adds a "Resent-Reply-To:" field, which consists
the field name, the optional comments and folding white space, the of the field name, the optional comments and folding white space, the
colon, and a comma separated list of addresses. colon, and a comma separated list of addresses.
obs-resent-from = "Resent-From" *WSP ":" mailbox-list CRLF obs-resent-from = "Resent-From" *WSP ":" mailbox-list CRLF
obs-resent-send = "Resent-Sender" *WSP ":" mailbox CRLF obs-resent-send = "Resent-Sender" *WSP ":" mailbox CRLF
obs-resent-date = "Resent-Date" *WSP ":" date-time CRLF obs-resent-date = "Resent-Date" *WSP ":" date-time CRLF
obs-resent-to = "Resent-To" *WSP ":" address-list CRLF obs-resent-to = "Resent-To" *WSP ":" address-list CRLF
obs-resent-cc = "Resent-Cc" *WSP ":" address-list CRLF obs-resent-cc = "Resent-Cc" *WSP ":" address-list CRLF
obs-resent-bcc = "Resent-Bcc" *WSP ":" obs-resent-bcc = "Resent-Bcc" *WSP ":"
(address-list / [CFWS]) CRLF (address-list / [CFWS]) CRLF
obs-resent-mid = "Resent-Message-ID" *WSP ":" msg-id CRLF obs-resent-mid = "Resent-Message-ID" *WSP ":" msg-id CRLF
skipping to change at line 1556 skipping to change at page 36, line 17
obs-resent-cc = "Resent-Cc" *WSP ":" address-list CRLF obs-resent-cc = "Resent-Cc" *WSP ":" address-list CRLF
obs-resent-bcc = "Resent-Bcc" *WSP ":" obs-resent-bcc = "Resent-Bcc" *WSP ":"
(address-list / [CFWS]) CRLF (address-list / [CFWS]) CRLF
obs-resent-mid = "Resent-Message-ID" *WSP ":" msg-id CRLF obs-resent-mid = "Resent-Message-ID" *WSP ":" msg-id CRLF
obs-resent-rply = "Resent-Reply-To" *WSP ":" address-list CRLF obs-resent-rply = "Resent-Reply-To" *WSP ":" address-list CRLF
As with other resent fields, the "Resent-Reply-To:" field is to be As with other resent fields, the "Resent-Reply-To:" field is to be
treated as trace information only. treated as trace information only.
4.5.7. Obsolete trace fields 4.5.7. Obsolete trace fields
The obs-return and obs-received are again given here as template The obs-return and obs-received are again given here as template
definitions, just as return and received are in section 3. Their full definitions, just as return and received are in section 3. Their
syntax is given in [SMTP]. full syntax is given in [RFC2821].
obs-return = "Return-Path" *WSP ":" path CRLF obs-return = "Return-Path" *WSP ":" path CRLF
obs-received = "Received" *WSP ":" name-val-list CRLF obs-received = "Received" *WSP ":" name-val-list CRLF
obs-path = obs-route-addr obs-path = obs-angle-addr
4.5.8. Obsolete optional fields 4.5.8. Obsolete optional fields
obs-optional = field-name *WSP ":" unstructured CRLF obs-optional = field-name *WSP ":" unstructured CRLF
5. Security Considerations 5. Security Considerations
Care needs to be taken when displaying messages on a terminal or Care needs to be taken when displaying messages on a terminal or
terminal emulator. Powerful terminals may act on escape sequences and terminal emulator. Powerful terminals may act on escape sequences
other combinations of ASCII control characters with a variety of and other combinations of ASCII control characters with a variety of
consequences. They can remap the keyboard or permit other modifications consequences. They can remap the keyboard or permit other
to the terminal which could lead to denial of service or even damaged modifications to the terminal which could lead to denial of service
data. They can trigger (sometimes programmable) answerback messages or even damaged data. They can trigger (sometimes programmable)
which can allow a message to cause commands to be issued on the answerback messages which can allow a message to cause commands to be
recipient's behalf. They can also effect the operation of terminal issued on the recipient's behalf. They can also effect the operation
attached devices such as printers. Message viewers may wish to strip of terminal attached devices such as printers. Message viewers may
potentially dangerous terminal escape sequences from the message prior wish to strip potentially dangerous terminal escape sequences from
to display. However, other escape sequences appear in messages for the message prior to display. However, other escape sequences appear
useful purposes (cf. [RFC-2045, RFC-2046, RFC-2047, RFC-2048, RFC-2049], in messages for useful purposes (cf. [RFC2045, RFC2046, RFC2047,
[ISO-2022]) and therefore should not be stripped indiscriminately. RFC2048, RFC2049, ISO2022]) and therefore should not be stripped
indiscriminately.
Transmission of non-text objects in messages raises additional security Transmission of non-text objects in messages raises additional
issues. These issues are discussed in [RFC-2045, RFC-2046, RFC-2047, security issues. These issues are discussed in [RFC2045, RFC2046,
RFC-2048, RFC-2049]. RFC2047, RFC2048, RFC2049].
Many implementations use the "Bcc:" (blind carbon copy) field described Many implementations use the "Bcc:" (blind carbon copy) field
in section 3.6.3 to facilitate sending messages to recipients without described in section 3.6.3 to facilitate sending messages to
revealing the addresses of one or more of the addressees to the other recipients without revealing the addresses of one or more of the
recipients. Mishandling this use of "Bcc:" has implications for addressees to the other recipients. Mishandling this use of "Bcc:"
confidential information that might be revealed, which could eventually has implications for confidential information that might be revealed,
lead to security problems through knowledge of even the existence of a which could eventually lead to security problems through knowledge of
particular mail address. For example, if using the first method even the existence of a particular mail address. For example, if
described in section 3.6.3, where the "Bcc:" line is removed from the using the first method described in section 3.6.3, where the "Bcc:"
message, blind recipients have no explicit indication that they have line is removed from the message, blind recipients have no explicit
been sent a blind copy, except insofar as their address does not appear indication that they have been sent a blind copy, except insofar as
in the message header. Because of this, one of the blind addressees their address does not appear in the message header. Because of
could potentially send a reply to all of the shown recipients and this, one of the blind addressees could potentially send a reply to
accidentally reveal that the message went to the blind recipient. When all of the shown recipients and accidentally reveal that the message
the second method from section 3.6.3 is used, the blind recipient's went to the blind recipient. When the second method from section
address appears in the "Bcc:" field of a separate copy of the message. 3.6.3 is used, the blind recipient's address appears in the "Bcc:"
If the "Bcc:" field sent contains all of the blind addressees, all of field of a separate copy of the message. If the "Bcc:" field sent
the "Bcc:" recipients will be seen by each "Bcc:" recipient. Even if a contains all of the blind addressees, all of the "Bcc:" recipients
separate message is sent to each "Bcc:" recipient with only the will be seen by each "Bcc:" recipient. Even if a separate message is
individual's address, implementations still need to be careful to sent to each "Bcc:" recipient with only the individual's address,
process replies to the message as per section 3.6.3 so as not to implementations still need to be careful to process replies to the
accidentally reveal the blind recipient to other recipients. message as per section 3.6.3 so as not to accidentally reveal the
blind recipient to other recipients.
6. Bibliography 6. Bibliography
[ASCII] American National Standards Institute (ANSI), Coded Character [ASCII] American National Standards Institute (ANSI), Coded
Set - 7-Bit American National Standard Code for Information Interchange, Character Set - 7-Bit American National Standard Code for
ANSI X3.4, 1986. Information Interchange, ANSI X3.4, 1986.
[ISO-2022] International Organization for Standardization (ISO), [ISO2022] International Organization for Standardization (ISO),
Information processing - ISO 7-bit and 8-bit coded character sets - Code Information processing - ISO 7-bit and 8-bit coded
extension techniques, Third edition - 1986-05-01, ISO 2022, 1986. character sets - Code extension techniques, Third edition
- 1986-05-01, ISO 2022, 1986.
[RFC-822] Crocker, D., Standard for the Format of ARPA Internet Text [RFC822] Crocker, D., "Standard for the Format of ARPA Internet
Messages. STD 11, RFC 822. August 1982. Text Messages", RFC 822, August 1982.
[RFC-2045] Freed, N. and Borenstein, N., Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies, RFC 2045, Extensions (MIME) Part One: Format of Internet Message
November 1996. Bodies", RFC 2045, November 1996.
[RFC-2046] Freed, N. and Borenstein, N., Multipurpose Internet Mail [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types, RFC 2046, November 1996. Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC-2047] Moore, K., Multipurpose Internet Mail Extensions (MIME) Part [RFC2047] Moore, K., "Multipurpose Internet Mail Extensions (MIME)
Three: Message Header Extensions for Non-ASCII Text, RFC 2047, November Part Three: Message Header Extensions for Non-ASCII Text",
1996. RFC 2047, November 1996.
[RFC-2048] Freed, N., Klensin, J., and Postel, J., Multipurpose Internet [RFC2048] Freed, N., Klensin, J. and J. Postel, "Multipurpose
Mail Extensions (MIME) Part Four: Format of Internet Message Bodies, RFC Internet Mail Extensions (MIME) Part Four: Format of
2048, November 1996. Internet Message Bodies", RFC 2048, November 1996.
[RFC-2049] Freed, N. and Borenstein, N., Multipurpose Internet Mail [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and Examples, RFC Extensions (MIME) Part Five: Conformance Criteria and
2049, November 1996. Examples", RFC 2049, November 1996.
[RFC-2119] Bradner, S., Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels, BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC-2234] Crocker, D., Editor, and Overell, P., Augmented BNF for [RFC2234] Crocker, D., Editor, and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF, November 1997. Syntax Specifications: ABNF", RFC 2234, November 1997.
[SMTP] Klensin, J., Editor, Simple Mail Transfer Protocol, Work In [RFC2821] Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC
Progress. 2821, March 2001.
[STD-3] Braden, R., Host Requirements, STD 3, RFC 1122 and RFC 1123, [STD3] Braden, R., "Host Requirements", STD 3, RFC 1122 and RFC
October 1989. 1123, October 1989.
[STD-12] Mills, D., Network Time Protocol, STD 12, RFC 1119, September [STD12] Mills, D., "Network Time Protocol", STD 12, RFC 1119,
1989. September 1989.
[STD-13] Mockapetris, P., Domain Name System, STD 13, RFC 1034 and RFC [STD13] Mockapetris, P., "Domain Name System", STD 13, RFC 1034
1035 November 1987. and RFC 1035, November 1987.
[STD-14] Partridge, C., Mail Routing and the Domain System, STD 14, RFC [STD14] Partridge, C., "Mail Routing and the Domain System", STD
974, January 1986. 14, RFC 974, January 1986.
7. Editor's Address 7. Editor's Address
Peter W. Resnick Peter W. Resnick
QUALCOMM Incorporated QUALCOMM Incorporated
5775 Morehouse Drive 5775 Morehouse Drive
San Diego, CA 92121-1714 San Diego, CA 92121-1714
USA USA
Phone: +1 858 651 4478
FAX: +1 858 651 1102
e-mail: [email protected]
[Editor's note: Grammar and syntax comments are welcome sent directly to Phone: +1 858 651 4478
the editor. Substantive comments on this document should be directed to Fax: +1 858 651 1102
the DRUMS working group. The subscription address is EMail: [email protected]
<[email protected]>.]
8. Acknowledgements 8. Acknowledgements
[TBD] Many people contributed to this document. They included folks who
participated in the Detailed Revision and Update of Messaging
Standards (DRUMS) Working Group of the Internet Engineering Task
Force (IETF), the chair of DRUMS, the Area Directors of the IETF, and
people who simply sent their comments in via e-mail. The editor is
deeply indebted to them all and thanks them sincerely. The below
list includes everyone who sent e-mail concerning this document.
Hopefully, everyone who contributed is named here:
Appendix A. Examples messages Matti Aarnio Barry Finkel Larry Masinter
Tanaka Akira Erik Forsberg Denis McKeon
Russ Allbery Chuck Foster William P McQuillan
Eric Allman Paul Fox Alexey Melnikov
Harald Tveit Alvestrand Klaus M. Frank Perry E. Metzger
Ran Atkinson Ned Freed Steven Miller
Jos Backus Jochen Friedrich Keith Moore
Bruce Balden Randall C. Gellens John Gardiner Myers
Dave Barr Sukvinder Singh Gill Chris Newman
Alan Barrett Tim Goodwin John W. Noerenberg
John Beck Philip Guenther Eric Norman
J. Robert von Behren Tony Hansen Mike O'Dell
Jos den Bekker John Hawkinson Larry Osterman
D. J. Bernstein Philip Hazel Paul Overell
James Berriman Kai Henningsen Jacob Palme
Norbert Bollow Robert Herriot Michael A. Patton
Raj Bose Paul Hethmon Uzi Paz
Antony Bowesman Jim Hill Michael A. Quinlan
Scott Bradner Paul E. Hoffman Eric S. Raymond
Randy Bush Steve Hole Sam Roberts
Tom Byrer Kari Hurtta Hugh Sasse
Bruce Campbell Marco S. Hyman Bart Schaefer
Larry Campbell Ofer Inbar Tom Scola
W. J. Carpenter Olle Jarnefors Wolfgang Segmuller
Michael Chapman Kevin Johnson Nick Shelness
Richard Clayton Sudish Joseph John Stanley
Maurizio Codogno Maynard Kang Einar Stefferud
Jim Conklin Prabhat Keni Jeff Stephenson
R. Kelley Cook John C. Klensin Bernard Stern
Steve Coya Graham Klyne Peter Sylvester
Mark Crispin Brad Knowles Mark Symons
Dave Crocker Shuhei Kobayashi Eric Thomas
Matt Curtin Peter Koch Lee Thompson
Michael D'Errico Dan Kohn Karel De Vriendt
Cyrus Daboo Christian Kuhtz Matthew Wall
Jutta Degener Anand Kumria Rolf Weber
Mark Delany Steen Larsen Brent B. Welch
Steve Dorner Eliot Lear Dan Wing
Harold A. Driscoll Barry Leiba Jack De Winter
Michael Elkins Jay Levitt Gregory J. Woodhouse
Robert Elz Lars-Johan Liman Greg A. Woods
Johnny Eriksson Charles Lindsey Kazu Yamamoto
Erik E. Fair Pete Loshin Alain Zahm
Roger Fajman Simon Lyall Jamie Zawinski
Patrik Faltstrom Bill Manning Timothy S. Zurcher
Claus Andre Farber John Martin
This section presents a selection of messages. These are intended to Appendix A. Example messages
assist in the implementation of this standard, but should not be taken
as normative; that is to say, although the examples in this section were
carefully reviewed, if there happens to be a conflict between these
examples and the syntax described in sections 3 and 4 of this document,
the syntax in those sections is to be taken as correct.
Messages are delimited in this section between lines of "----". The This section presents a selection of messages. These are intended to
"----" lines are not part of the message itself. assist in the implementation of this standard, but should not be
taken as normative; that is to say, although the examples in this
section were carefully reviewed, if there happens to be a conflict
between these examples and the syntax described in sections 3 and 4
of this document, the syntax in those sections is to be taken as
correct.
Messages are delimited in this section between lines of "----". The
"----" lines are not part of the message itself.
A.1. Addressing examples A.1. Addressing examples
The following are examples of messages that might be sent between two The following are examples of messages that might be sent between two
individuals. individuals.
A.1.1. A message from one person to another with simple addressing A.1.1. A message from one person to another with simple addressing
This could be called a canonical message. It has a single author, John This could be called a canonical message. It has a single author,
Doe, a single recipient, Mary Smith, a subject, the date, a message John Doe, a single recipient, Mary Smith, a subject, the date, a
identifier, and a textual message in the body. message identifier, and a textual message in the body.
---- ----
From: John Doe <[email protected]> From: John Doe <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: Fri, 21 Nov 1997 09:55:06 -0600 Date: Fri, 21 Nov 1997 09:55:06 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
If John's secretary Michael actually sent the message, though John
If John's secretary Michael actually sent the message, though John was was the author and replies to this message should go back to him, the
the author and replies to this message should go back to him, the sender sender field would be used:
field would be used:
---- ----
From: John Doe <[email protected]> From: John Doe <[email protected]>
Sender: Michael Jones <[email protected]> Sender: Michael Jones <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: Fri, 21 Nov 1997 09:55:06 -0600 Date: Fri, 21 Nov 1997 09:55:06 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
A.1.2. Different types of mailboxes A.1.2. Different types of mailboxes
This message includes multiple addresses in the destination fields and This message includes multiple addresses in the destination fields
also uses several different forms of addresses. and also uses several different forms of addresses.
---- ----
From: "Joe Q. Public" <[email protected]> From: "Joe Q. Public" <[email protected]>
To: Mary Smith <[email protected]>, [email protected], Who? <[email protected]> To: Mary Smith <[email protected]>, [email protected], Who? <[email protected]>
Cc: <[email protected]>, "Gaint; \"Big\" Box" <[email protected]> Cc: <[email protected]>, "Giant; \"Big\" Box" <[email protected]>
Date: Tue, 1 Jul 2003 10:52:37 +0200 Date: Tue, 1 Jul 2003 10:52:37 +0200
Message-ID: <[email protected]> Message-ID: <[email protected]>
Hi everyone. Hi everyone.
---- ----
Note that the display names for Joe Q. Public and Giant; "Big" Box Note that the display names for Joe Q. Public and Giant; "Big" Box
needed to be enclosed in double-quotes because the former contains the needed to be enclosed in double-quotes because the former contains
period and the latter contains both semicolon and double-quote the period and the latter contains both semicolon and double-quote
characters (the double-quote characters appearing as quoted-pair characters (the double-quote characters appearing as quoted-pair
construct). Conversely, the display name for Who? could appear without construct). Conversely, the display name for Who? could appear
them because the question mark is legal in an atom. Notice also that without them because the question mark is legal in an atom. Notice
[email protected] and [email protected] have no display names associated with also that [email protected] and [email protected] have no display names
them at all, and [email protected] uses the simpler address form without associated with them at all, and [email protected] uses the simpler
the angle brackets. address form without the angle brackets.
A.1.3. Group addresses A.1.3. Group addresses
---- ----
From: Pete <[email protected]> From: Pete <[email protected]>
To: A Group:Chris Jones <[email protected]>,[email protected],John <[email protected]>; To: A Group:Chris Jones <[email protected]>,[email protected],John <[email protected]>;
Cc: Undisclosed recipients:; Cc: Undisclosed recipients:;
Date: Thu, 13 Feb 1969 23:32:54 -0330 Date: Thu, 13 Feb 1969 23:32:54 -0330
Message-ID: <[email protected]> Message-ID: <[email protected]>
Testing. Testing.
---- ----
In this message, the "To:" field has a single group recipient named A In this message, the "To:" field has a single group recipient named A
Group which contains 3 addresses, and a "Cc:" field with an empty group Group which contains 3 addresses, and a "Cc:" field with an empty
recipient named Undisclosed recipients. group recipient named Undisclosed recipients.
A.2. Reply messages A.2. Reply messages
The following is a series of three messages that make up a conversation The following is a series of three messages that make up a
thread between John and Mary. John firsts sends a message to Mary, Mary conversation thread between John and Mary. John firsts sends a
then replies to John's message, and then John replies to Mary's reply message to Mary, Mary then replies to John's message, and then John
message. replies to Mary's reply message.
Note especially the "Message-ID:", "References:", and "In-Reply-To:" Note especially the "Message-ID:", "References:", and "In-Reply-To:"
fields in each message. fields in each message.
---- ----
From: John Doe <[email protected]> From: John Doe <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: Fri, 21 Nov 1997 09:55:06 -0600 Date: Fri, 21 Nov 1997 09:55:06 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
When sending replies, the Subject field is often retained, though
When sending replies, the Subject field is often retained, though prepended with "Re: " as described in section 3.6.5.
prepended with "Re: " as described in section 3.6.5.
---- ----
From: Mary Smith <[email protected]> From: Mary Smith <[email protected]>
To: John Doe <[email protected]> To: John Doe <[email protected]>
Reply-To: "Mary Smith: Personal Account" <[email protected]> Reply-To: "Mary Smith: Personal Account" <[email protected]>
Subject: Re: Saying Hello Subject: Re: Saying Hello
Date: Fri, 21 Nov 1997 10:01:10 -0600 Date: Fri, 21 Nov 1997 10:01:10 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
In-Reply-To: <[email protected]> In-Reply-To: <[email protected]>
References: <[email protected]> References: <[email protected]>
This is a reply to your hello. This is a reply to your hello.
---- ----
Note the "Reply-To:" field in the above message. When John replies to Note the "Reply-To:" field in the above message. When John replies
Mary's message above, the reply should go to the address in the "Reply- to Mary's message above, the reply should go to the address in the
To:" field instead of the address in the "From:" field. "Reply-To:" field instead of the address in the "From:" field.
---- ----
To: "Mary Smith: Personal Account" <[email protected]> To: "Mary Smith: Personal Account" <[email protected]>
From: John Doe <[email protected]> From: John Doe <[email protected]>
Subject: Re: Saying Hello Subject: Re: Saying Hello
Date: Fri, 21 Nov 1997 11:00:00 -0600 Date: Fri, 21 Nov 1997 11:00:00 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
In-Reply-To: <[email protected]> In-Reply-To: <[email protected]>
References: <[email protected]> <[email protected]> References: <[email protected]> <[email protected]>
This is a reply to your reply. This is a reply to your reply.
---- ----
A.3. Resent messages A.3. Resent messages
Start with the message that has been used as an example several times: Start with the message that has been used as an example several
times:
---- ----
From: John Doe <[email protected]> From: John Doe <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: Fri, 21 Nov 1997 09:55:06 -0600 Date: Fri, 21 Nov 1997 09:55:06 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
Say that Mary, upon receiving this message, wishes to send a copy of
Say that Mary, upon receiving this message, wishes to send a copy of the the message to Jane such that (a) the message would appear to have
message to Jane such that (a) the message would appear to have come come straight from John; (b) if Jane replies to the message, the
straight from John; (b) if Jane replies to the message, the reply should reply should go back to John; and (c) all of the original
go back to John; and (c) all of the original information, like the date information, like the date the message was originally sent to Mary,
the message was originally sent to Mary, the message identifier, and the the message identifier, and the original addressee, is preserved. In
original addressee, is preserved. In this case, resent fields are this case, resent fields are prepended to the message:
prepended to the message:
---- ----
Resent-From: Mary Smith <[email protected]> Resent-From: Mary Smith <[email protected]>
Resent-To: Jane Brown <[email protected]> Resent-To: Jane Brown <[email protected]>
Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800 Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800
Resent-Message-ID: <[email protected]> Resent-Message-ID: <[email protected]>
From: John Doe <[email protected]> From: John Doe <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: Fri, 21 Nov 1997 09:55:06 -0600 Date: Fri, 21 Nov 1997 09:55:06 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
If Jane, in turn, wished to resend this message to another person, she If Jane, in turn, wished to resend this message to another person,
would prepend her own set of resent header fields to the above and send she would prepend her own set of resent header fields to the above
that. and send that.
A.4. Messages with trace fields A.4. Messages with trace fields
As messages are sent through the transport system as described in As messages are sent through the transport system as described in
[SMTP], trace fields are prepended to the message. The following is an [RFC2821], trace fields are prepended to the message. The following
example of what those trace fields might look like. Note that there is is an example of what those trace fields might look like. Note that
some folding white space in the first one since these lines can be long. there is some folding white space in the first one since these lines
can be long.
---- ----
Received: from x.y.test Received: from x.y.test
by example.net by example.net
via TCP via TCP
with ESMTP with ESMTP
id ABC12345 id ABC12345
for <[email protected]>; 21 Nov 1997 10:05:43 -0600 for <[email protected]>; 21 Nov 1997 10:05:43 -0600
Received: from machine.example by x.y.test; 21 Nov 1997 10:01:22 -0600 Received: from machine.example by x.y.test; 21 Nov 1997 10:01:22 -0600
From: John Doe <[email protected]> From: John Doe <[email protected]>
skipping to change at line 1900 skipping to change at page 47, line 4
Received: from machine.example by x.y.test; 21 Nov 1997 10:01:22 -0600 Received: from machine.example by x.y.test; 21 Nov 1997 10:01:22 -0600
From: John Doe <[email protected]> From: John Doe <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: Fri, 21 Nov 1997 09:55:06 -0600 Date: Fri, 21 Nov 1997 09:55:06 -0600
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
A.5. White space, comments, and other oddities A.5. White space, comments, and other oddities
White space, including folding white space, and comments can be inserted White space, including folding white space, and comments can be
between many of the tokens of fields. Taking the example from A.1.3, inserted between many of the tokens of fields. Taking the example
white space and comments can be inserted into all of the fields. from A.1.3, white space and comments can be inserted into all of the
fields.
---- ----
From: Pete(A wonderful \) chap) <pete(his account)@silly.test(his host)> From: Pete(A wonderful \) chap) <pete(his account)@silly.test(his host)>
To:A Group(Some people) To:A Group(Some people)
:Chris Jones <c@(Chris's host.)public.example>, :Chris Jones <c@(Chris's host.)public.example>,
[email protected], [email protected],
John <[email protected]> (my dear friend); (the end of the group) John <[email protected]> (my dear friend); (the end of the group)
Cc:(Empty list)(start)Undisclosed recipients :(nobody(that I know)) ; Cc:(Empty list)(start)Undisclosed recipients :(nobody(that I know)) ;
Date: Thu, Date: Thu,
13 13
Feb Feb
1969 1969
23:32 23:32
-0330 (Newfoundland Time) -0330 (Newfoundland Time)
Message-ID: <[email protected]> Message-ID: <[email protected]>
Testing. Testing.
---- ----
The above example is aesthetically displeasing, but perfectly legal. The above example is aesthetically displeasing, but perfectly legal.
Note particularly (1) the comments in the "From:" field (including one Note particularly (1) the comments in the "From:" field (including
that has a ")" character appearing as part of a quoted-pair); (2) the one that has a ")" character appearing as part of a quoted-pair); (2)
white space absent after the ":" in the "To:" field as well as the the white space absent after the ":" in the "To:" field as well as
comment and folding white space after the group name, the special the comment and folding white space after the group name, the special
character (".") in the comment in Chris Jones's address, and the folding character (".") in the comment in Chris Jones's address, and the
white space before and after "[email protected],"; (3) the multiple and folding white space before and after "[email protected],"; (3) the
nested comments in the "Cc:" field as well as the comment immediately multiple and nested comments in the "Cc:" field as well as the
following the ":" after "Cc"; (4) the folding white space (but no comment immediately following the ":" after "Cc"; (4) the folding
comments except at the end) and the missing seconds in the time of the white space (but no comments except at the end) and the missing
date field; and (5) the white space before (but not within) the seconds in the time of the date field; and (5) the white space before
identifier in the "Message-ID:" field. (but not within) the identifier in the "Message-ID:" field.
A.6. Obsoleted forms A.6. Obsoleted forms
The following are examples of obsolete (that is, the "MUST NOT The following are examples of obsolete (that is, the "MUST NOT
generate") syntactic elements described in section 4 of this document. generate") syntactic elements described in section 4 of this
document.
A.6.1. Obsolete addressing A.6.1. Obsolete addressing
Note in the below example the lack of quotes around Joe Q. Public, the Note in the below example the lack of quotes around Joe Q. Public,
route that appears in the address for Mary Smith, the two commas that the route that appears in the address for Mary Smith, the two commas
appear in the "To:" field, and the spaces that appear around the "." in that appear in the "To:" field, and the spaces that appear around the
the jdoe address. "." in the jdoe address.
---- ----
From: Joe Q. Public <[email protected]> From: Joe Q. Public <[email protected]>
To: Mary Smith <@machine.tld:[email protected]>, , jdoe@test . example To: Mary Smith <@machine.tld:[email protected]>, , jdoe@test . example
Date: Tue, 1 Jul 2003 10:52:37 +0200 Date: Tue, 1 Jul 2003 10:52:37 +0200
Message-ID: <[email protected]> Message-ID: <[email protected]>
Hi everyone. Hi everyone.
---- ----
A.6.2. Obsolete dates A.6.2. Obsolete dates
The following message uses an obsolete date format, including a non- The following message uses an obsolete date format, including a non-
numeric time zone and a two digit year. Note that although the day-of- numeric time zone and a two digit year. Note that although the
week is missing, that is not specific to the obsolete syntax; it is day-of-week is missing, that is not specific to the obsolete syntax;
optional in the current syntax as well. it is optional in the current syntax as well.
---- ----
From: John Doe <[email protected]> From: John Doe <[email protected]>
To: Mary Smith <[email protected]> To: Mary Smith <[email protected]>
Subject: Saying Hello Subject: Saying Hello
Date: 21 Nov 97 09:55:06 GMT Date: 21 Nov 97 09:55:06 GMT
Message-ID: <[email protected]> Message-ID: <[email protected]>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
A.6.3. Obsolete white space and comments A.6.3. Obsolete white space and comments
White space and comments can appear between many more elements than in White space and comments can appear between many more elements than
the current syntax. Also, folding lines that are made up entirely of in the current syntax. Also, folding lines that are made up entirely
white space are legal. of white space are legal.
---- ----
>From : John Doe <jdoe@machine(comment). example> From : John Doe <jdoe@machine(comment). example>
To : Mary Smith To : Mary Smith
__
<[email protected]> <[email protected]>
Subject : Saying Hello Subject : Saying Hello
Date : Fri, 21 Nov 1997 09(comment): 55 : 06 -0600 Date : Fri, 21 Nov 1997 09(comment): 55 : 06 -0600
Message-ID : <1234 @ local(blah) .machine .example> Message-ID : <1234 @ local(blah) .machine .example>
This is a message just to say hello. This is a message just to say hello.
So, "Hello". So, "Hello".
---- ----
Note especially the second line of the "To:" field. It starts with two Note especially the second line of the "To:" field. It starts with
space characters. Therefore, it is considered part of the folding as two space characters. (Note that "__" represent blank spaces.)
described in section 4.2. Also, the comments and white space throughout Therefore, it is considered part of the folding as described in
addresses, dates, and message identifiers are all part of the obsolete section 4.2. Also, the comments and white space throughout
syntax. addresses, dates, and message identifiers are all part of the
obsolete syntax.
Appendix B. Differences from earlier standards Appendix B. Differences from earlier standards
This appendix contains a list of changes that have been made in the This appendix contains a list of changes that have been made in the
Internet Message Format from earlier standards, specifically [RFC-822] Internet Message Format from earlier standards, specifically [RFC822]
and [STD-3]. Items marked with an asterisk (*) below are items which and [STD3]. Items marked with an asterisk (*) below are items which
appear in section 4 of this document and therefore can no longer be appear in section 4 of this document and therefore can no longer be
generated. generated.
1. Period allowed in obsolete form of phrase. 1. Period allowed in obsolete form of phrase.
2. ABNF moved out of document to [ABNF]. 2. ABNF moved out of document to [RFC2234].
3. Four or more digits allowed for year. 3. Four or more digits allowed for year.
4. Header field ordering (and lack thereof) made explicit. 4. Header field ordering (and lack thereof) made explicit.
5. Encrypted header field removed. 5. Encrypted header field removed.
6. Received syntax loosened to allow any token/value pair. 6. Received syntax loosened to allow any token/value pair.
7. Specifically allow and give meaning to "-0000" time zone. 7. Specifically allow and give meaning to "-0000" time zone.
8. Folding white space is not allowed between every token. 8. Folding white space is not allowed between every token.
9. Requirement for destinations removed. 9. Requirement for destinations removed.
10. Forwarding and resending redefined. 10. Forwarding and resending redefined.
11. Extension header fields no longer specifically called out. 11. Extension header fields no longer specifically called out.
12. ASCII 0 (null) removed.* 12. ASCII 0 (null) removed.*
13. Folding continuation lines cannot contain only white space.* 13. Folding continuation lines cannot contain only white space.*
14. Free insertion of comments not allowed in date.* 14. Free insertion of comments not allowed in date.*
15. Non-numeric time zones not allowed.* 15. Non-numeric time zones not allowed.*
16. Two digit years not allowed.* 16. Two digit years not allowed.*
17. Three digit years interpreted, but not allowed for generation. 17. Three digit years interpreted, but not allowed for generation.
18. Routes in addresses not allowed.* 18. Routes in addresses not allowed.*
19. CFWS within local-parts and domains not allowed.* 19. CFWS within local-parts and domains not allowed.*
20. Empty members of address lists not allowed.* 20. Empty members of address lists not allowed.*
21. Folding white space between field name and colon not allowed.* 21. Folding white space between field name and colon not allowed.*
22. Comments between field name and colon not allowed. 22. Comments between field name and colon not allowed.
23. Tightened syntax of in-reply-to and references.* 23. Tightened syntax of in-reply-to and references.*
24. CFWS within msg-id not allowed.* 24. CFWS within msg-id not allowed.*
25. Tightened semantics of resent fields as informational only. 25. Tightened semantics of resent fields as informational only.
26. Resent-Reply-To not allowed.* 26. Resent-Reply-To not allowed.*
27. No multiple occurrences of fields (except resent and received).* 27. No multiple occurrences of fields (except resent and received).*
28. Free CR and LF not allowed.* 28. Free CR and LF not allowed.*
29. Routes in return path not allowed.* 29. Routes in return path not allowed.*
30. Line length limits specified. 30. Line length limits specified.
31. Bcc more clearly specified. 31. Bcc more clearly specified.
Appendix C. Notices Appendix C. Notices
Full Copyright Statement Intellectual Property
Copyright (C) The Internet Society (2000). All Rights Reserved. The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
This document and translations of it may be copied and furnished to Full Copyright Statement
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works. However, this document itself
may not be modified in any way, such as by removing the copyright notice
or references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet
Standards process must be followed, or as required to translate it into
languages other than English.
The limited permissions granted above are perpetual and will not be Copyright (C) The Internet Society (2001). All Rights Reserved.
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS This document and translations of it may be copied and furnished to
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK others, and derivative works that comment on or otherwise explain it
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT or assist in its implementation may be prepared, copied, published
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT and distributed, in whole or in part, without restriction of any
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR kind, provided that the above copyright notice and this paragraph are
FITNESS FOR A PARTICULAR PURPOSE. included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
Intellectual Property The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
The IETF takes no position regarding the validity or scope of any This document and the information contained herein is provided on an
intellectual property or other rights that might be claimed to pertain "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
to the implementation or use of the technology described in this TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
document or the extent to which any license under such rights might or BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
might not be available; neither does it represent that it has made any HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
effort to identify any such rights. Information on the IETF's procedures MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
with respect to rights in standards-track and standards-related
documentation can be found in BCP-11. Copies of claims of rights made
available for publication and any assurances of licenses to be made
available, or the result of an attempt made to obtain a general license
or permission for the use of such proprietary rights by implementors or
users of this specification can be obtained from the IETF Secretariat.
This document expires July 26, 2000. Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
 End of changes. 240 change blocks. 
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