If not yet done, turn on OAuth2 authentication in your account settings for the Gmail account. That goes for both, the incoming, and outgoing server. After a Thunderbird restart you'll be prompted for your Google credentials, and you'll have to allow Thunderbird to access your Gmail account.

If not yet done, turn on OAuth2 authentication in your account settings for the Gmail account. That goes for both, the incoming, and outgoing server. After a Thunderbird restart you'll be prompted for your Google credentials, and you'll have to allow Thunderbird to access your Gmail account.

Do I do this at Gmail or on Thunderbird for the email address? Or both?

It bothers me that other than emails from Google, there is no mention of needing to do this from Thunderbird - or a simplified process by Thunderbird to address this - as there must be many, many thousands of Thunderbird users that have gmail email coming into Thunderbird and and this change by Gmail/Google effects everyone of those users. There are a lot of users out there that will have no idea what to do - or even what Google is saying in these emails that are going to lose access to their email in two months!

OAuth2 for gmail has been supported in TB for a few years. For mail accounts, simply follow the above instructions to change the authentication method, restart TB, enter your account password in the OAuth window. Cookies must be accepted in TB Preferences for OAuth to work.

For Google calendars, unsubscribe the existing calendar, then add it from File/New/Calendar...On the Network...enter the gmail address...calendars are autodetected...enter the password in the OAuth window.

Similarly for Contacts, Remove the address book from Address Book if it's present, File/New/CardDAV Address Book...enter the gmail address...Contacts are autodetected...enter the password in the OAuth window.

I was unable to send emails through Thunderbird (TB) that was linked to my Gmail account. Suddenly all my passwords seemed wrong. And then when I started fiddling, I couldn't receive or send emails through TB. This occurred today June 7, 2022.

Please excuse. my inability to speak/type in a techy way. I'm terrible with computers, but I seem to have solved my issue. So I am hoping that if I post this then it might help someone who tends to not fiddle with their computer unless absolutely necessary. I'm a Mac person.

Go into TB -> Preferences -> Privacy & Security -> Saved passwords and remove them all. Go into TB -> Preferences -> Account settings -> Server settings -> switch Authentication method to OAuth2 I did this with all my gmail accounts. Then scroll down to Outgoing Server (SMTP) and I chose Google Mail and then Edit. Switched the Authentication method to OAuth2. Quit TB and restart it. Have your passwords handy because you will need them to link everything up.

So now a few hours later, I am able to receive and send emails through TB.

p.s. I did follow what some others had written, but I had trouble understanding where to find what they were talking about. (Like where is the Outgoing Server?). Yes, I am that dweeb-y with computers.

This works for email but not for chat with a Google Talk account. How do you use oAuth2 with that?

I reset Thunderbird to OATH2 and it was working, but after upgrading to v10.2, Thunderbird will no longer download GMail. It won't even attempt to download.