Did you search the passwords store for all instances of the password? Use the box at the top to make it display all logins related to your account.

Failing that, you can re-set Thunderbird's store of email logins and passwords (so be sure you know them all before going any further.) Find Thunderbird's profile, (Help|Troubleshooting Information), close Thunderbird and delete the files k3.db and signons.sqlite.

Thanks Zenos. First paragraph wasn't entirely clear and the answer's probably No I didn't. I used the Tools>Options>Security>Passwords and deleted both accounts listed. Not sure what I would search in the top ("Search") box.

However I moved on to the second. k3.db was (I hope!) key3.db in mine. Deleted both and the only change is that instead of the status bar reading "Connected ..." for a few seconds it now seems to be on permanently!

The box at the top is a search/filter. If you type anything into it, it will show logins that include what you typed. So putting in your email domain, for instance, should reveal all logins associated with your email service, including incoming and outgoing, both old and new.

Yes, it should have been key3.db

But I take it we're no further on?

Have you updated Thunderbird recently? Do you use a firewall that needs to be told about this?

Thanks again. The only e-mail addresses are associated with my domain - atlantichouse.org.uk. I've typed in "atlantichouse" and it returns no data, so I guess they've all been deleted.

I don't use a firewall; I have updated Thunderbird earlier today as part of my attempt to solve this problem (it began when both my wife and I were unable to access mail, using different laptops - which I suppose suggests that the problem may not be at our end - though surely it should still be asking me for a PW) but not for some time previously.

A pragmatic route forward at this point may be to set the account up again (I mean a second instance of the account; don't delete the old one, yet…) in Thunderbird…

Something else to try:

Tools|Options|Advanced|General→Config Editor

If challenged, promise that you'll be careful.

Type password into the filter box

Look for security.ask_for_password - is it set to 1? Double-click it and enter 1 if not. Close and restart Thunderbird…