A general rule of thumb: if Thunderbird worked for years and suddenly asks for a password, there is nothing wrong with Thunderbird. Some users may retype it, but it won’t help and they may risk losing (forgetting) the original one and/or cause an additional issue. Being able to access webmail is some kind of evidence of that, and does not guarantee POP or IMAP servers to be accessible by clients. Not to say bad things about BT, but this would [/questions/1066925 not be] the first time their customers suffer outages for email. Therefor you could check their service status either [http://downdetector.co.uk/problems/bt-british-telecom here], [http://www.bt.com/help/servicestatus here] or [https://downtoday.co.uk/bt-email/ here]. If the above does not apply and BT would suddenly require you to change your email connection settings, try [/questions/1020686 setting up the account again] in your current profile while keeping the existing one, or [[Using Multiple Profiles|create a second profile]] to test that with, rather than changing current connection settings. Keep in mind that if setting it up again works, it may take some time to get all messages synchronized, and require some disk space. If you use POP, be sure to set up TB to leave messages on the server in that test setup (i.e. do not allow it to get messages immediately / before entering the password). If you use IMAP, let it finish in order to prevent accidental changes due to aborting that may affect the regular setup.