How to implement email correlation with subject and body modification?

I have a system that sends mail.

I have a system that receives mail.

I need to identify that a received mail correlates with the one the other system sent. The particular thing here is that either the subject or the body can be modified.

I thought on putting some hash in the header of the sent email, but I don't know where this could be added

Don't you hav开发者_JAVA百科e any clue?

As you did not supply enough detail for a language specific answer, I will explain the general approach.

You can add a custom header to your outbound email, using x-vendor-header style for the header (start with x- to mark it as an extension, then vendor- for your company and end with the header name. The can be a unique identifier for the email message.

You can look for this header in your inbound process to identify the message.

I've finally found the solution:

Most email's servers support to put something after the username using '+' as separator. So I can encrypt some id and decrypt it when is replied looking on the from address.

example:

neuquino+encryptedID123421234@gmail.com

I hope this can help someone else with the same problem