@OffByOne said:
You don't need anything more than a correct References header to have proper threading.
This is patently untrue based on what people reported on meta.
Before:
Message-ID: <54752ba335286_633fee205cc454883a2@tiefighter6-virtual_host.mail>
In-Reply-To: <topic/91@talk.thumbtack.io>
References: <topic/91@talk.thumbtack.io>
After:
Message-ID: <topic/22572/86235@meta.discourse.org>
In-Reply-To: <topic/22572@meta.discourse.org>
References: <topic/22572@meta.discourse.org>
Which corresponds almost exactly to what GitHub was sending...
Message-ID: <discourse/discourse/pull/3006/c64666078@github.com>
In-Reply-To: <discourse/discourse/pull/3006@github.com>
References: <discourse/discourse/pull/3006@github.com>
the only difference is the message-id field was not specified, we were letting the mailserver set it.