Does waitrose use Oauth to authenticate? If not, then I would not expect reverting to 60.9.0 to help - because Oauth is the only patch in 60.9.1.

Unless ... some other product is interfering, then going back might help.

I don't know what waitrose uses. I think it is actually John Lewis under a relay.

I installed 60.8.1 but this has not fixed the problem. I don;t undertand why this has suddenly stopped working. Nothing has changed apart from the TB update.

https://support.mozilla.org/kb/cannot-send-messages

Before I tried resetting SMTP server or creating new account, waitrose login started working again. No TB Updates so problem must have been at Waitrose server despite tech support assuring me no issues.