Can you atribute a Reply to a Mail via the Mail Header?

Question

Is it possible to include into the E-Mail-Header an information such as a client ID in a way, that if the person replies to this mail and even if the titel or content of the original mail is cleaned out, this client ID is transfered with the reply?

Situation: we have a client relationship system which allows to send e-Mails to clients. Yet we do wonder if it is possible that we attribute an incoming mail (being a reply to a former send mail) automatically to the client even if this client did change the titel, deleted the Mail Body of the mail he is answering to and/or is using a different sender e-mail-adress then the one marked in our system.

Usually the header is generated by the sender. Means a reply does not send the old header but generates a new header.

Is there a way to transfer such an information as a code of 5 numbers from the old header to the new?

Thanks for your answers.

Answer 1

If you include a Message-ID header, most clients will include an In-Reply-To header in a reply even if the subject is changed.

http://en.wikipedia.org/wiki/Email#Header_fields

Answer 2

Andrew's answer of using the Message ID and In-Reply-To headers works well however with any solution like this it's not 100% possible to ensure the chain as you never quite know what the users mail client will do.

Another alternative is to use a unique from address for each email [email protected]. You can then associate the from address with the old conversation and bring in any new replies that way.