I assume this is about a corporate BT Connect (Office 365) account, which apparently uses Outlook servers, correct? Did you make sure the server settings are still entered as instructed [https://btbusiness.custhelp.com/app/answers/detail/a_id/18746/kw/18746/c/5169/ here], and for POP? According to [https://business.forums.bt.com/t5/Email/BT-Connect-IMAP-email-settings/td-p/74989 this info], BT Connect still doesn’t allow IMAP in case you are trying to set it up, but I could be wrong. If you did not change anything and the issue occurred suddenly, it may be (or have been?) a temporary issue with the servers and allowing BT logins. _{Side note: it would be best if you edit your previous message and its title to remove your full email address, or at least the first part of it.}