Recently, when I try to quit Mail, the Quit menu option is actually disabled and the keyboard shortcut doesn't work (it "beeps" just like when you try to do anything that isn't permitted). Screenshot for proof:

Any idea what's causing this and how I can prevent it from happening? The only "solution" I've found is to force quit Mail...
I'm running Mail 6.2 on 10.8.2.

Mail.appis syncing, cleaning something up, etc, and hangs. My experience is that it seldom goes back to a state in which you can quit it with Command-Q, so I usually revert to pressing Command-Shift-Option-Esc for a couple of seconds... – jaume Nov 16 '12 at 11:40