Troubleshooting - OSX - Mail.app
Rebuild Mail.app's Index of Mail (analog to Window Outlook's OST)
Quit Mail.app.
~/Library/Mail/V2/MailData/
Rename/delete/move files beginning with ENVELOPE, EXTERNAL, or FLAG.
Launch Mail.app.
Wait.
Quit Mail.app.
~/Library/Mail/V2/MailData/
Rename/delete/move files beginning with ENVELOPE, EXTERNAL, or FLAG.
Launch Mail.app.
Wait.