moderated Re: How on earth does Groups.io thread a topic?
On Tue, Jan 3, 2017 at 2:42 PM, Brian Vogel <britechguy@...> wrote:
I've traced things and figured out what happened. The system worked as designed, but perhaps the algorithm needs a tweak. We do threading two ways. One is by looking for the threading headers in the message (In-Reply-To and References), and use those to figure out which thread a message belongs to. These are standard headers that all mail clients should use, but alas some don't.
If a message does not have those headers, we then look for a message with the same subject within the last week. If there is one, we assume this is a reply to that message and thread it.
Now, here's the rub. We only look for matching subjects when the incoming message subject starts with 'Re:'. Because we don't want to accidentally thread messages that should be in different threads. In your thread's case, one message came through without threading headers and without a subject that started with 'Re:', which caused a new thread to start.
So, should we remove the 'Re:' restriction? I could make the argument that the person that sent the reply message, without any threading headers and with a subject line that did not start with 'Re:' needs to upgrade his email client, because that's severely broken behavior.