I have tried the following: 1. Changed the authentication method from OAuth2 to Normal Password (for both incoming(IMAP) and outgoing(SMTP)).

For IMAP as well as SMTP you should stick with OAuth2.

Screenshot attached

The screenshot doesn't load for me. In any case, use the server settings as per Google's advice. https://support.google.com/mail/answer/7126229?hl=en

3. Tried this "trick"

There are no magic tricks. Follow the Google troubleshooting steps. https://support.google.com/accounts/answer/6009563

Note that this error comes after a very long time (4-6 minutes) after clicking the "Done" button.

The long timeout looks a bit suspicious. Is there a networking problem? Do you use a third party firewall?

Also have a look at these troubleshooting steps. https://support.mozilla.org/kb/cannot-receive-messages

Thanks for the reply christ1.

I have checked that the configuration is as per google's advice.

As for the troubleshooting tips given by Google, their first advice is to turn ON less secure apps, which has already been done. Their second advice is regarding two-step verification process, which is NOT even enabled in my case. My gmail login is done using only the password. So this step doesn't help.

As for the troubleshooting steps on https://support.mozilla.org/kb/cannot-receive-messages, none of it helps, either.

No, I don't have any firewalls on the system, also there are no network issues at all.

PS: I'm able to see the image attachment.

As for the troubleshooting tips given by Google, their first advice is to turn ON less secure apps, which has already been done.

This step is listed underneath the section 'Your device or app might not support Google’s security standards'.

While I admit this may not be obvious, 'OAuth2' authentication is what's considered as the Google’s security standard. In other words, with OAuth2 the 'less secure apps' setting doesn't apply.

The next section underneath '2-Step Verification is not supported by the app' doesn't apply either, because with OAuth2 Thunderbird also supports 2-Step verification natively.

So what's left being relevant in your case is the section underneath 'Still having trouble signing in?'.

Did you check these steps?

Did you create an app password for Thunderbird at some point, and trying to use that? Use the main account password.

Can you confirm your account is to be set up as IMAP?

Are you using the Thunderbird version provided by your distribution, or the vanilla version from Mozilla?

Thanks again, christ1.

Yeah, I have checked the steps under "Still having trouble signing in?". Those steps did not work. Still the same error after about 4-5 minutes. (in fact this is nearly the step described in the "trick" I was talking about..)

No, I have never created an App pasword. I am entering the main password. My password has 14 characters with one special character (exclamation mark !) in it. I did read a post regarding a problem with some special characters. Can you please confirm this could not be the problem?

Yes, I am trying to configure it as an IMAP account. The incoming server address is imap.gmail.com.

I have tried both versions. My distribution provided TBird 45 (which gave the same error). I am now trying the steps using TBird 52.1.1 downloaded from the official website.

I have figured out the problem - it's my ISP. I am in a university campus and they aparently don't have "open ports" for Thunderbird, etc.. I don't know why or what it means, but it's not a TBird issue.

Thanks.

Good. Please mark your post as 'Solution' for this topic. Thank you.