When initial Service Desk email has other recipients, thread responses to original email
Description
When an email is sent with multiple recipients, one of which is the Service Desk, replies to the initial email will also include the Service Desk on the recipients list. Currently, this results in the reply generating a new ticket, which presents something of a footgun when adding the Service Desk to a workflow that previously included direct customer contact.
Proposal
It would be nice if, when an email arrives at the service desk, it was checked for In-Reply-To (and perhaps References) headers, matching the Message-ID headers of messages that had already opened service tickets.
