Any way to assign a unique ID to sent e-mail via headers or meta data?

[imekul]

I have a WordPress blog, and I set up a custom PHP script where I can pipe an e-mail sent to a certain address, having it execute this PHP script that parses the e-mail and then posts the WordPress post.

 

This works just fine.

 

As soon as the post is entered (or if another author makes a post), I receive an e-mail with the text of the post.  The subject of the e-mail contains the WordPress post ID.  The reason I do that is because I have the script set up where I can quote a given post by simply replying to the corresponding e-mail.  Since each subject has its own ID, which is tied to the WP post, this works fine.

 

What I'm trying to do is figure out a more elegant way to include a unique identifier -- that is, the post ID -- in some place OTHER than the subject.  For instance, if there was a meta tag or something where I can include a unique identifier, yet it doesn't have to show up in the subject.

 

So an ideal solution would be to take the post ID (say 12345) that would normally show up in the subject, and instead put it in some hidden variable or parameter that is part of the e-mail's headers or meta data.  That way, that data would still be accessible by the PHP script, and could be linked to the correct post, but it also frees up the subject line.

 

Any ideas on how I could accomplish this?  Basically, I'm looking for a way to assign a unique message ID to each e-mail -- some way to track which e-mail is being replied to.  It would be ideal if it was something that was hidden and not shown in the subject or body of the e-mail.

 

Thanks for reading!