Since moving from Yahoo to BT mail i am having a bizarre issue with my email on Apple Mail on ipad (i got rid of the BT mail app because it is awful!)
When on wifi it sends and receives with no issue. When on 3g it will receive, but will not send unless the password is re-entered in the outgoing server screen... but even then, that only works around 10% of the time. If you connect to another phone by personal hotspot, it sends with no issue...
Any ideas??