I’ve had a number of calls over the past few days from clients with MobileMe accounts who are having trouble sending otherwise innocuous mail. No settings have changed, the address is correct, there are no attachments (or they are small), and the e-mail should just go out. But it doesn’t. Instead, Mail spins for a few minutes, then displays an error window.
If this describes your experience over the past week, rest assured, it’s not you, it’s them.