We have some business partners who run their own ticketing system, and in order to track issues on our end we do it in FB, while they do it in their own system. Their system strips out the (Case #####) from the subject line when they reply to us, so FogBugz creates a new case for every reply.
It gets really bad if they send an automated "Thank you for annoying us" email, so now FB creates TWO new cases for every exchange. One case is for the useless thank-you message, and the other case is where the conversation has drifted to. After only a couple of back-n-forth exchanges there are DOZENS of FB cases that have to be rounded up and marked as dupes, and we STILL don't have a single case from which to see the whole history from.
They do, however, include their own ticket number in the subject, although it'll look something like:
RE: Blah Blah Blah (Ticket #12345)
Can FogBugz honor third-party ticket numbers and keep that correspondence within the same case, even if FB's case number gets stripped out of the subject line?