Should work again with maildir.
Some bugfixes to indexes (possibly fixing the still persisting maildir sync errrors?)
Enabled cache file again. If client asks about something that can be cached for future, it's done. There's currently no smart logic about when not to do it or when to cache more than was asked for future use. Currently nothing is ever deleted from cache. Currently it's disabled if mmap_disable = yes.
Removed UIDPLUS extension after all. It needs more thinking with maildir, because for performance reasons new messages are given UIDs once at the end transaction rather than separately for each one. So, the UID would have to be 0 temporarily until transaction is committed. But the current API make the new messages visible without syncing, and then the sequences don't match anymore and we can't get the UIDs. So, this one needs thinking, mostly from API designing point of view.