I'm presuming you have correct server settings which means you are using oauth2 for Authentication Method for both incoming and outgoing. That means gmail is not expecting a normal password, so it's likely to fail.

To test your normal password you need to logon to your gmail webmail account via a browser. If you get access to account then you know that password is perfectly ok. If you cannot get access then there will be a forgotten password link which you need to use and follow instructions to regain access to webmail account and then you can reset the password.

Are you using a pop or imap mail account?

You may need to reset the password for both incoming and outgoing.

• In Settings > Privacy & Security
• Passwords section
• click on 'saved Passwords'
• Click on 'Show Passwords'.

If you see a 'windows security' window asking for password: When you start up computer you get asked for a user account password to see desktop - windows wants you to enter that password.

To reset a password: You may see imap:// or mailbox:// or smtp:// or oauth:// for that gmail user name/email address. Remove all the lines that are for that gmail email address.

Exit Thunderbird and allow a few moments for all background processes to complete. Restart Thunderbird At the gmail prompt enter the correct normal password Then it may ask for you to allow Thunderbird access so click on 'Accept' or it might say 'Allow'

This should reset the stored oauth for the account.

Dear Toad-Hall, I changed my Authentication Method for both incoming and outgoing server to oauth2. Used to be Normal Password. I logged on to gmail webmail account via a browser and could see and process my email so password is okay. I deleted all saved passwords related to my gmail email address. I exited Thunderbird and then re-entered Thunderbird. Computer said: "Sign in to continue to Thunderbird email" and prompted the correct email address. I clicked in Next and got an error "Google 400. That's an error. The server cannot process the request because it is malformed. It should not be retried. That's all we know." What next step should I follow now? I still can't use Thunderbird which was working fine yesterday. Thanks.

That sounds like you have only just altered the Authentication Method.

You have to perform a few checks to ensure a gmail account can be set up for Oauth. It needs cookies allowed and a couple of other checks are worth doing at the same time.

Firewall: Access Firewall which may be controlled by the OS or by an Anti-Virus program you installed. Thunderbird must be set up as an allowed program.

VPN Please check computer and Anti-Virus product to see if a VPN has been enabled. Server does not like VPN, it will block access. So switch off VPN or create a split tunnelling and set up Thunderbird to use it.

'Localhost' If you use a program that uses 'localhost' - some people manage websites so might use something like Apache Xampp - Switch it off until Oauth has been set up.

In Thunderbird

• Settings > Privacy & Security
• WEb Content
• Select : 'Accept cookies from sites'
• Accept third party cookies 'Always'
• Click on 'Exceptions' button
• Set up: https://accounts.google.com as 'Allow'
• Click on 'Save Changes'

Scroll down to Passwords

• Click on 'Saved Passwords'
• Remove any line that mentions username = gmail email address you are trying to reset.
• Click on 'Close'

Exit Thunderbird and allow a few moments for background processes to complete and then restart Thunderbird. This time when you start Thunderbird and it asks for password you should get the correct window to allow authentication.