Use Thread-Index email header field to add incoming emails as comments on existing tickets instead of creating duplicate tickets
It would be awesome if we could choose to use the Thread-Index email header field on incoming email to reduce duplicate tickets. It happens quite often that people CC our IT ticket queue email address on email conversations, and we get a ticket for every reply-all. If the Thread-Index header field was used, then all of the reply-alls would come in as comments on the ticket created from the first email in that thread, rather than duplicate tickets.
Jon Saam commented
I've seen other systems use email headers (message id in one particular instance) to identify incoming emails that belong to an already existing ticket.