I had a message stuck sending in yahoo so I deleted the account and reentered it. Then it appeared fine but all of a sudden it showed there were actually 3 open mailboxes 2frozen from before with an old time and one up to date with the unsent message stuck in the nonexistent outbox. I can send messages now but i was hoping someone may know how can I close the 2 mailboxes lingering in the background And get rid of the message that won't send?
I can't say if it will work, but there is no harm in trying "killing the app":
While in the Mail app, hold the Sleep button until you see the "Slide to power off" screen. Let go of the Sleep button, then press and hold the Home button until you get back to the Home screen (should be about 3 or 4 seconds).
This stops the application and clears up any memory leak issues that the app is causing.
Nothing will be deleted or reset, so there is no harm trying this.
I had this problem and tried doing this and it worked for me!!!