ipad suddenly cannot send mail
asking on behalf of my wife.... her ipad and phone have been been working normally but suddenly she has found that emails will not send from the ipad: there is a message "cannot send mail, username or password is incorrect". On pressing send the "swooshing" noise occurs but the message ends up in the outbox but not the sent or drafts box.
Mail is still received on both phone and ipad, and mail will send from the iphone. The mail account is @bt.com. Passwords were not changed recently, and being apple of course I cannot see what the passwords are. I have tried re-entering the passwords which I have stored elsewhere and there is no brief indication of what each character is as it is being entered in the password field when I re-entered it.
Suggestions please??
iPhone SE, iOS 14