Have been using gmail on Thunderbird for years. But suddenly I find incoming and outgoing messages have stopped working. Every time get the message that the password is incorrect when I know it is correct since is working on other platforms. Looked online wasting hrs trying to fix. Server originally set to normal password, flipped to Oauth2 and removed all saved IMAP, Oauth2 and SMTP passwords as suggested on a previous mozilla answer to a similar problem. This has fixed the incoming email problem so I can now receive emails but cannot send so the problem remains. Cannot remove the account and reload since a large number of the 10,000's of emails, are held on Thunderbird alone. The total randomness of the problem, with no warning whatsoever, Is extremely inconvenient and no doubt lost on those IT professionals who strive to change what already works. Any assistance would be greatfully received.