I've been having this strange problem with my Yahoo! mail today on the iPhone. I'll compose an email, hit the Send button, the "Sending... " bar will appear with one tick of progress on it for about 2 or 3 seconds, then the screen goes black (except for the top toolbar) and it kicks me back to the main home screen! And when I go back into the Mail app, the message is still in my Drafts folder like it's unsent but the message actually goes through. Is anyone else experiencing this?