A quick < 3 minutes of perusing didn't see anything fruitful so in the bugs, but perhaps my search terms were wonky ...
I'd like to request that you add a header to Bitbucket.org project-generated emails. Maybe for comments it's something like:
Or for pull-requests, it's something like:
The bit after the '+' is not perhaps necessary, just nice. The important thing for my uses would be the ability to sort messages on something less crude than the content of the subject field.