About two weeks ago, my Dad's email password started getting rejected on his laptop. He uses Mozilla Thunderbird client. It had been working perfectly well up to this date.
His password was fine though, because he could login via webmail interface using the same password. We tried resetting it and things worked again briefly but, now it has stopped working again. His password is being rejected even though we know it works. Webmail still works and he can pick up mail on his iPad as well.
At one point he could receive mail but not send it.
I've read numerous related issues in these forums and have tried the changing of the SMTP and POP3 server names to ones ...yahoo.co.uk ones but this still does not work.
This sounds like the regular but intermittent password rejection problem that has afflicted btinternet email for the best part of a decade. Sometimes logging into webmail can 'clear' it, but otherwise don't change any settings (assuming you know them to be ok) and just wait. It usually clears itself up in hours or at most a day or so.