It's just broken again for me.
Wants me to re-enter password but won't accept it. Client doesn't work this time either.
I've got it working again. It was to do with the login for MyBT, which has always been a separate login for email for me.
During the problems it said the login for MyBT was out of date and had to be changed. Changing that has also changed the login for email.
It looks like they both work off the same password now but I still have to login again if I go to MyBT.
Now I've just got to update my other devices.