To me that does not sound like a fix, just being lucky, but you are right you might have replaced mail with one without that bug. And it make no sense to me to turn off automatic updates, your mail app should be kept up to date.
I think that I may have gone into the account section of mail, removed the current account, reentered it, and so replaced the old and may be corrupted profile with a new one.
But who cares, you are up and runing, i hope this recepe also works for TechGust.
B.t.w, we still don't know if he uses the same mail client.