I could not send emails from my iPad, it would try to send then after a while tell me my email address or password was wrong, phoned BT they try to sort the problem tell you everything is fine, but you still have the same problem on the iPad, use BT web mail or your computer to access you email and it will work, but its slow and thats the problem, the iPad times out before the BT server responds because its too slow, get on to BT and tell them, keep at them till its fixed.
Watch out for the reply from BT "your iPad need to be returned to the manufacturer" this is BT response to fob you off, keep at them, keep telling them the email server is responding too slowly then cross your fingers until its put right.