Currently, if the pledge amount stays the same, multiple derailments for the same goal on different days have identical subject lines. This means that if an email client sorts threads by subject line, they get put in the same thread.
I request that the date be put in the subject line, giving each derailment a unique subject and a separate thread.
Threads based on subject lines is completely ridiculous and wrong and that’s exactly what the References header in RFC 1036 (section 2.2.5) was defined for:
2.2.5. References
This field lists the Message-ID’s of any messages prompting the
submission of this message. It is required for all follow-up
messages, and forbidden when a new subject is raised.
I just checked my Gmail account and Beeminder notification emails are threaded for me, too.
To be fair, most of the places I see this are in Eep! emails which aren’t such a big deal, since incrementing pledges make it less likely to happen for derails.