Why is Safari saying BT email deleted, when it is actually there?
If you have problems with the email from BT, I recommend checking the FAQ page provided by the BT developers.
Access the following page to read more about the BT and the email problems: http://bt.custhelp.com/app/answers/detail/a_id/44932/~/all-about-bt-mail
Additionally, try removing the BT email and then adding it back. It's possible that Safari might have some bugs when used with an email account.