i do not have a bt account and am trying to access my talk21 email which I have logged in via the bt app since yesterday. I have tried using the suggested email of username.t21@bibternet.com and this is not working either. I am getting the error as attached.
If you do not have a BT account or you do not pay for Premium Mail you may well have lost the email address.
Presumably it is a typo when you wrote username.t21@bibternet.com. If not, try username.t21@btinternet.com