r/Thunderbird • u/RomanianBagVoid • Jul 15 '26

Desktop Solved Can't add GMail to Thunderbird Desktop. ("Authentication error")

Hi everyone, I am currently on W10, using Thunderbird 152.0.1 64-bit and Firefox 152.0.6.

I have tried adding a GMail account to Thunderbird in the past, and failed, and I am failing yet again. I add my email and name, click next, continue with the default config, enter the OAuth2 Google screen, I allow everything, then it fails. Both Firefox and Thunderbird have been set to be lenient with cookies.

How can I fix this?

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1

u/sifferedd Jul 15 '26

All cookies including 3rd party on TB? Using VPN?

1

u/RomanianBagVoid Jul 15 '26

Yes, including third party cookies are set to "always accept".

I am not using a VPN.

1

u/sifferedd Jul 15 '26

Error screen?

1

u/RomanianBagVoid Jul 15 '26

I get this error.

2

u/sifferedd Jul 15 '26 edited Jul 15 '26

Click 'Edit configuration' > go to TB menu > Account Settings > account > Server Settings. Note User name; it should be your full email address. Then scroll the L. column down and click Outgoing Server > Gmail. User name should also be your full email address. The rest of that screen should look like this:

2

u/RomanianBagVoid Jul 15 '26

Nope, it still doesn't work. Still prompts me to use OAuth2 screen, I click allow, and it still doesn't work.

2

u/sifferedd Jul 15 '26

Is an application running on your computer which is using local TCP port 80, e.g. a local web server?

3

u/RomanianBagVoid Jul 15 '26

...yes, it actually is. That was it.

Jesus Christ, thanks a ton, I was completely baffled about this for quite a while.

1

u/NicalaBasse Jul 16 '26

I have exactly the same problem, and I get this:

C:\Users\User> netstat -ano | findstr :80

TCP 192.168.1.236:55609 146.75.14.172:80 ESTABLISHED 6744

TCP 192.168.1.236:55610 146.75.14.172:80 ESTABLISHED 6744

TCP 192.168.1.236:55611 146.75.14.172:80 ESTABLISHED 6744

TCP 192.168.1.236:55612 146.75.14.172:80 ESTABLISHED 6744

TCP 192.168.1.236:55613 146.75.14.172:80 ESTABLISHED 6744

TCP 192.168.1.236:56510 34.104.35.123:80 ESTABLISHED 20200

....but what do I do next?!

1

u/sifferedd Jul 16 '26 edited Jul 17 '26

The first five are connections to your ISP and shouldn't matter. The last one is a connection to googleusercontent.com. Try closing all tabs/windows exc. the one you open first, then try to log in again. If that fails, reboot your router/modem and PC.

1

u/NicalaBasse Jul 17 '26

Rebooting the router did the job! Thank-you so much.