Sorting threads/conversations

I assume you have clicked on the “Date Received” column header. Within a thread it cannot be reversed because of the strict threading used (parent-child). It wouldn't make any sense. A different threading mode is needed and that is something I (still) have not implemented. The only other option is to disable threading (in the View menu).

There's already a series of other tickets touching this subject (in various ways). I'll mark this one as accepted too and I'll update it if an alternative threading mode is implemented.