What headers have to be sent
Emails sent from Tuleap contains those headers:
MessageID: userid-artifactid-hash-randomid@tuleap.tld
Reply-to: artifacts@tuleap.tld
When user reply to the message, the reply contains a reference to the MessageID (tested with mutt, to be tested with outlook, thunderbird and gmail).
References: <userid-artifactid-hash-randomid@tuleap.tld> <…> <…>
Then just add an entry in aliases to be able to parse the incoming email.
forge__XXXX: "| /path/to/script/… "
How to generate the hash
The hashish email is given by the class Tracker_Artifact_MailGatewayRecipientFactory.
Change on trackers
Mail generation in trackers must be done user by user instead of "group of user"