Good point. Absolutely, I did. (Had to. It won’t talk to Envelope Index otherwise.) I made sure that Tester had Read & Write permissions on the copied files. And then went to the top of the folder (~/Library/Mail) and copied the permissions to subfolders (Apply to enclosed items) to boot.

Trick: this (below) kb article mentions an extra crucial step that solved the problem. After I replaced the original Envelope Index file to double check everything else was fine then pulled it again and a (Key step) MAC-XXXXXX folder from a MobileMe account, THEN let Mail rebuild the index (took 3 times as long, nearly 40 seconds) file and it was fine. And correct.

So I made another copy of my real Mail folder and tried the simpler Mail menu Mailbox:Rebuild on the problem (Sent had ghosts that wouldn’t delete, just get greyer) and that worked on that one folder.

All better now. So now I get to fix Address Book not syncing with MobileMe only on this account.

Apple Kb Article: http://support.apple.com/kb/TS1907