Suggestion for Email: X-Thread-ID

I was just thinking, as I read over my twitter stream, that one of the best
features for Gmail is indeed the threading capabilities.  To have all of your messages that pertain
to a certain subject/discussion listed as a thread with individual messages; allows for much better message
management, and makes it much easier to find what you’re looking for.

But one way to make
this even easier, would be an introduction of a new header into emails:

X-Thread-ID

This would be the MD5 of the subject and timestamp, or something along those lines to generate an
ID that would be very or completely unlikely to accidentally be recreated.

This would
make it super easy for mail clients and servers alike to keep track of threads.

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