I waste a lot of time in Thunderbird looking for conversations whose subject isn't shown in the threaded list, because Thunderbird threads are too sticky.
Thunderbird keeps messages in the same thread that shouldn't be, including:
- A reply or reply-all where the subject line has been changed to indicate a branch in the discussion onto a new topic.
- A message created to start an entirely new conversation, but using reply-all to an existing email in order to use some or all of the addressees without retyping them all.
These messages should start a new thread, or at least give the user a configuration option to make that the default.
