How to edit a message subject to add tags?

Apr 22, 2013 at 11:28 AM
I want to add certain tags to messages in my mailbox. I have an application that makes automatic tickets from new mails, but there is a blacklist. If an email is blacklisted, and thus there is not ticket created from it, then I want to add something like [BLACKLISTED] to the messages subject so it is very clear what happened. How can I achieve this?