Is it a scam?

First of all, make sure that you actually got the letter from a court. This might very well be a scam - it sure sounds like one. Do this to verify that the letter is real:

1. Make sure that the name of the court correspond to a real court.
2. Find contact information to that court through some independent method (i.e. not using any information in the letter).
3. Contact them and ask them if they did in fact send the letter.

If it is not a scam

If it is not a scam, I see three possibilities:

• The person accusing you of the threats never recieved the emails, and have forged the evidence. That would not be hard to do. (An investigation of the email headers will not help here, since they can also be forged.)
• Someone has spoofed your email adress, and has sent emails that appear to come from you. This is by no means impossible. (An investigation of the email headers could be useful here.)
• Someone has hacked your email account (perhaps you used the same password on a site that was breached), sent the emails, and then deleted all traces (e.g. removed them from the sent items folder). (An investigation of the email headers would not help here, since the email is in fact sent from your adress. Access logs from your email provider could prove useful, though.)

In any case, what you need to do is get some legal advice.

(Assuming US) No court is going to pre-emptively demand a settlement of $20K for a misdemeanor(!!!) before you've even had a chance to testify. Furthermore, threats are a criminal matter; this isn't a property dispute-- the police would have questioned you long ago, before this ever went to court.

If this letter truly claims to have been issued by a court (and you're not misreading it), it's bogus. Call the magistrate's office for the issuing municipality and verify.

If it came from a lawyer's office, it's a shakedown. Don't sweat it. Consult your own-- they may well tell you to just ignore it. The victim/scammer can demand whatever they want; it doesn't mean you're obligated to pay.

Either way, someone's targeting you (possibly the "victim") and one of your first steps needs to be filing a police report to document the fact that someone is either making false accusations or committing criminal behavior in your name. It's easy, free, and sets a precedent that you can later point back to if this escalates or happens again.

Whether or not this is bogus, under no circumstance should you talk to the (alleged) victim.

It is actually very easy to send an email and to enter the email you would like it to show as sent from.

Here is one that i found on a quick google search

I do believe it is a scam like all the others said. But it is very possible for someone to send emails that appear to come from you.

Due to the nature of electronic mails, anyone can send a mail with any name from NASA to FBI to your neighbour. You need to raise the court's attention to this.

Get the court release the full emails, including its headers. The headers will tell that the emails did not go through your mail server (or the mail server you use). If you are using an email giant like google, yahoo, etc, like 99% of other people use, it's pretty easy to prove your right, because the absence of DKIM is a clear sign of spoofing. If not, you might have to prove that you did not have access to the server the mail is originated from.

P.S.: Modern email providers automatically use DKIM and SPF for validating authority, and some of them (gmail for example) constantly mark emails as spam whose senders don't use these. I think it's by now a widely accepted standard, and exchanging mails without these techniques is just like regular mail where you claim to be yourself just by writing your name on the envelope.