I am astounded Apple could have such a serious issue in something as fundamental to computing as its flagship Mail program.
This issue (or erroneous message counts, unread counts, sporadic not-so-smart folders, etc.) when I updated to Mavericks. Perhaps even the release before that (10.8.x). Today I jumped up to latest Yosemite. Same problem. 27000+ people have looked at this forum thread. No solution from Apple.
With that off my chest...
I am disinclined to remove and re-add, or to reindex my mail accounts as I have a few gig of data (mail going back a long way). It's a massive amount of downloading to keep repeating whilst attempting to resolve Apple's Mail issues.
Would someone please advise, does deleting the Mail envelop files result in a full reindex (much like the Reindex option from within Mail itself)? i.e. Resulting in a full redownload of the emails. ?
Thank you,
Jonathan