I, too, lost my Outbox, but for a different reason.
I composed 15 messages on an airplane and "sent" them, which put them in the 'Outbox'. When I arrived home, I:
- Cmd-A (to select all 15 messages from Outbox)
- tried to send them (via Cmd-Shift-D)
- answered 'Yes' to "Send all these messages?"
- noticed that they were gone. G-O-N-E. Nowhere to be found.
I eventually found them in:
~/Library/Mail/V2/Mailboxes/Outbox.mbox/some-UUID-here/Data
By selecting a time that was an hour (or so) before their disappearance, I was able to restore them from my online backup service to a different location (e.g. ~/Desktop/mail_app_message_restore). I'm betting that TimeMachine could do something similar.
The messages were distributed (hashed, actually) among many directories, but when I issued this command from the command line, I found all 15 missing messages:
$ cd ~/Desktop/mail_app_message_restore # or where you restored them
$ find Outbox.mbox -type f
Outbox.mbox/14D01FAB-9E5D-420D-8507-240D11CEC6D4/Data/5/4/1/Messages/145098.emlx
[ 14 other files ... ]
$
Notice that the hash directories (e.g. Data/5/4/1) are just the reverse of the top few digits of the message filename. All of mine were in this 5/4/1 directory, but your numbers will be different. It's a big directory structure, but there were only a few messages sprinkled through it.
Best of luck!!!
Michael
P.S. Notice the side benefits of automagic backups? What a great feature! I'm so glad that it got a snapshot as soon as I got online, but that there was time before I tried to send them. I think TimeMachine would have been even better about taking offline backups before I reconnected to the network.
Best Answer
No. This isn't possible with a standard install of OSX Mail.app.
What you can do, as I am sure you are already well aware of, is set up multiple signatures, and manually select the signature that you desire to use. What you can do in the case of wanting no signature is set up a "signature" labeled "Empty", and then put nothing in there. Then have that set to default, or the other way around.