have you configured the SMTP server to use oAuth credentials and authorized cookies if they have been disabled? That is Googles preferred authentication and using anything else is getting harder and harder.

So, this is the send config and this is what I believe is the cookies setup... Please check and correct if wrong?! Thanks.

When you're prompted for a password in the OAuth window, enter the account password, not an app password. Remove the passwords or oauth tokens from Saved Passwords in Edit/Preferences/Privacy & Security, restart TB, and complete the OAuth process again.

When you're prompted for a password in the OAuth window, enter the account password, not an app password. Remove the passwords or oauth tokens from Saved Passwords in Edit/Preferences/Privacy & Security, restart TB, and complete the OAuth process again.

Yep, have done all that, multiple times...

OK, seems to be working... The config is: Recieve ; SSL/Normal Password using App Password Send ; SSL/Normal password using App Password BUT, I am still getting prompts for OAuth2 Gmail Authentication, https://drive.google.com/file/d/1Fc72Tb2yAYckaB44MKS5Kkp-vA4etc73/view?usp=sharing (which I am just closing! - was previously trying to authenticate through this, and believe that is why I was failing to send!) Anyone know how I can get rid of these Oauth2 authentication prompts - seem to still come up randomly after dismissing it on login... (ie in what file on disk is this stored - can I delete a config file and then just login and re-enter passwords??)

Thanks.

If you want to access gmail in TB, it's best to use OAuth authentication. Once the process is completed, an oauth:// token is stored in Saved Passwords in TB Options, and you shouldn't see any more authentication prompts, unless you change the account password on the gmail website.