The most common cause of this is a dialog from Mail located off-screen, or on a second display. You can use Expose to find the offending dialog and dismiss it.
The past couple of days I'll have Mail open but when I try and X out of it nothing happens. When I try and quit Mail nothing happens. Is there a way for me to force quit it?
Has this been happening to anyone else? It's getting annoying.
You can force quit an application by right (or ctrl) clicking on it's icon in the dock. The menu that pops up has the force quit command.
The past couple of days I'll have Mail open but when I try and X out of it nothing happens. When I try and quit Mail nothing happens. Is there a way for me to force quit it?
Has this been happening to anyone else? It's getting annoying.
Using IMAP? I have had this issue quite often. I too have found no offending off screen prompt. Based upon this and other behaviors I think Mail has some issues with IMAP.