how can sendmail server add auto increment number on the same subject

Question

I have a sendmail server. I want to add an auto increment number on the subject when everyone reply the mail.

For example:

1. I send a mail and the subject is "aaaa", the server can switch the subject to "aaaa" [000]
2. when my partner reply the mail, the server can switch the subject to "aaaa" [001]

I am a chinese guy. My Enghlish is so bad. Apologize for any inconvenience caused.

Answer 1

You would need sendmail to rewrite emails through a milter. Some serious assembly will be required, and you probably want to make sure that your milter-code doesn't accidentally break stuff, even in the weirdest circumstances for any other email. On the other hand, just matching the Subject against a regular expression and replacing it should not be too difficult.

I doubt there is ready-made software for your problem.