Mail continuously states in activity window "saving xx of yy drafts", even with no drafts in draft box. Related: in box messages often empty.

Mail continuously states in activity window "saving xx of yy drafts", for days now. No drafts in draft box, rebuilt many times. Related issue: In box messages often are empty. If I select reply to them (trying to get the message up in the reply) it maps to a previously opened email.

Yesterday for first time on another Mac I use often, it had not synched with email for days and many messages were there showing unread, and many had been moved to a subfolder on my home Mac were. not mapped to the destination folder.

Finally, in the folders titled "on my Mac" under "recovered messages (iCloud)" it is full of mail that had not been moved to the right folders, though the original IS in the right folder.

I'd like to Clea rate cache or some system file to allow everything to rebuild. Suggestions?