well clearly the issue is not the password then. Have you checked the other account settings against what your provider (freenetname) expects you to use.

Actually the issue definitely _WAS_ the password.

I contacted the provider ("freenetname" became "madasafish" a long time ago and then "madasafish" was sold to PlusNet, which is part of the British Telecom ["BT"] group) and they manually reset the password back to what it was supposed to be and then everything resumed working normally; but I had not changed it myself and freenetname/madasafish/plusnet had no record of any password change in the past two years, and yet a few hours before I posted this enquiry your app suddenly stopped showing my Inbox and was demanding that I enter the password.

So the Thunderbird app had corrupted its own record of what it thought the password should be.

Every time I try to open Thunderbird I get an error message saying ’Login to server mail.freenetname.co.uk with username "*******@freenetname.co.uk failed” and telling me to either “Retry” or “Enter New Password” - neither of which gives me access to my inbox).

Are you now saying you were reentering it incorrectly?

I was re-entering it correctly but Thunderbird wasn't recognising it because its internal record of the password had been corrupted. Are you being deliberately obtuse?

Before a user asks/report such problems, they should know exactly their internet/email provider and they should check their connection data in the accounts settings. Otherwise they are being obtuse. Thunderbird does exactly what a user declares in the account settings.

I've done all that, so I am NOT being obtuse. I didn't change the password myself and my ISP has confirmed they didn't change it either, and they don't even have any record of it being changed. And yet it did change very suddenly two days ago, and the only possible explanation is that the Thunderbird mail client must have done this by itself.

as Thunderbird has a store of passwords everyone assumes it must be the problem. But what about the password vault your anti virus has? Not all have them, but I have lost count of the number of folks in this forum complaining about password issues when their anti virus was quietly substituting the wrong thing after they clicked ok. Nortons was the last I heard of quietly doing it's best to ensure connectivity failed. But any sort of password vault is prone to errors. Basically not suitable for daily use in most cases.

I don't use Norton.