Gmail can be difficult. This URL may help. It's not 'officially' recognized by Mozilla, but it's clearly written. https://www.supertechcrew.com/thunderbird-oauth2-gmail/ I hope it helps you.

Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

Thank you David for the link to post. I had actually already found and tried it, with no success, but tried again, also with no success. When I create a GMail account in Thunderbird (Windows 10) it reports 'Configuration found in Mozilla ISP database' and takes me to Google Account Sign-in. I enter my password and Allow Thunderbird access. But then I always get the error message 'Unable to log in at server' I have tried this many times, and Thunderbird shows no paswords saved. All I get is the 'Unable to log in at server' error. I am wondering if something has changed in Thunderbird and/or Google security since the guidance posts were written. If so it seems kinda important to get Thunderbird working with GMail! Of if someone can point me to something stupid that I am doing, then I shall be very grateful.

One simple but essential point - if you are using OAuth2 with any account, you must have Thunderbird set to allow cookies. If not, Thunderbird cannot save the one-time authorization code from Google/AOL/Yahoo, and just keeps asking every time. Check this question's solution for a picture of the setting you need. https://support.mozilla.org/en-US/questions/1307545 Please report back if that worked, or if not.

Just a suggestion: Review the basics, that you have OAUTH2 for security and that you have specified in gmail.com to allow IMAP or POP access. Just to check, I downloaded and installed a separate copy of Thunderbird and set up a new gmail account. It went through the same steps you described and then worked, so something is afoul here. For what it's worth to you, problems with gmail setups are a large number of the support requests received here.

Many thanks for response. Much appreciated. Might I suggest that it might mightily help, not just me but everyone else with GMail/Thunderbird issues, now and in the future, if you could post screen grabs of all server settings for a working GMail setup (with email IDs masked of course). That way we all know what every adjustable setting should look like.

@Barry I had to reinstall Windows 10 and that wiped my apps (another story) All my gmail accounts were working fine in TB before the reinstall. I too have tried all the above suggestions and also unistalled my AV (Kaspersky). The furtest I've got is the attaced message.

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Thanks for the ongoing input. I am beginning to fear that Thunderbird is a dead duck for some email systems, such as GMail. And if it can't handle ubiquitous GMail it has no value as a working tool. It may sound churlish to complain about a free system but TB does ask for donations - which the developers can hardly expect to receive if the system does not work and they don't say 'we know, we are working on it'.

TB works just fine with Gmail here.

Of if someone can point me to something stupid that I am doing, then I shall be very grateful.

Just read what has been suggested, and respond to it. https://support.mozilla.org/en-US/questions/1364363#answer-1474158

Barry, I do feel your frustration, but I have done tech support with several other email clients and the confusion with Gmail setups pervails. It's easiest when starting from scratch to set up an account. Yes, developers seek donations, because it is with support that they can continue to refine TB. If people think they can contribute nothing until the system works to their satisfaction, the product will never be developed. Support is vital. There used to be an extensive inventory of email clients, but most have disappeared. Thunderbird needs our continued support.

Hi Barry and David, I note that the one error message that has been posted is specifically to do with an expired certificate. Just putting that out in text hoping someone will see it. Barry - there are lots of resources supporting how to connect Gmail and Thunderbird, it works for many people and both Thunderbird support articles and Gmail support articles provide lots of information. However given the error message you posted, it might not be anything to do with the specific email provider you are connecting to. I can't hep with the expired certificate issue so I'll leave you with David to work on that.