I like to keep sent mail, I file it periodically. Unfortunately, I must have changed my settings to delete mail older than 1 month. So now I'm trying to restore mail from a backup. (Don't ask me why I can't enter Time Machine. I guess I should ask that as a separate question. I can back up but not enter Time Machine! So I'm trying to do this manually). I can find Sent Messages.ewsmbox Sent Items.ewsmbox and I can read that they have lots of good stuff in them, but when I copy them into Mailboxes, they don't show up in my Sent folder when I go to Mail.