I've been sending/receiving bt.com emails through my GMail account for at least six years, but then got a 'too many emails on the server' msg. So I deleted a load off the bt.com server, logged out of GMail, logged in again, but no change.
So then I deleted the bt.com account off GMail and tried adding it again, using the settings listed on bt.com. GMail throws it out every single time, sometimes with an error msg, but usually by defaulting to the inbox view.
Can anyone help, pls?
Are you presently a BT Broadband customer or are you paying for your email through a BT Premium email account?
If neither of the above your email account may have been downgraded to a BTMail Basic account which can not be used with an email client or via another email service's web page.
See link
https://www.bt.com/help/email/bt-email-products