Sequoia OS and BT Internet email - Outlook for Mac; Airmail; Mail

It appears that since upgrading my Mac to the Sequoia OS I now have terrible trouble using BTinternet email.

Outlook for Mac stopped sending emails. I deleted the account and it is now impossible to add it back.

Airmail still receives BTInternet email, sometimes starts the day sending emails but then invariably stops sending them stating that my credentials are incorrect.

Mail crashes after a few minutes.

I am still running Sonoma OS on my 2019 Macbook Air and Outlook for Mac continues to operate as before.

Any useful input?