Are you using an Apple device? I found this long conversation that describes similar to what you describe. Only Apple device users seem to be affected. There are a number of suggested fixes, but it's not clear to me if any of them are the one true magic bullet.

https://forums.xfinity.com/conversations/email/apple-device-email-clients-not-working-with-comcastnet-accounts/6913dbb2ed2c3f53707a1ee9

I am using Win 10, I have tried all the remedies that was offered in other treads, notting has solve my connection problem.

Notting from the experts? Still can not connect to the Comcast email account. Any help from Thunderbird support? Does anyone have a phone number for the support team?

From the Thunderbird FAQ:

https://support.mozilla.org/en-US/kb/thunderbird-faq

Where can I get help with using Thunderbird?

Support is available primarily in these ways:

- The web-based Knowledge Base of many articles, for example the article you are reading now.

- Thunderbird's support forum where you can ask a question, or search for issues and answers if you didn't find the answer in the Knowledge Base.

- Various other communication sources, some of which cover special topics.

Thunderbird does not provide direct support via email, fax, chat, phone, remote, nor paid services, so be wary of offers of paid support, and also please report scams that you think are suspicious. Instead we rely on our volunteer community to help users. We hope that you, a Thunderbird user, will become a Thunderbird community member.

Thank you, Lin, for this NON-ANSWER, answer. It means we are on our own. You got a problem? Go find your own answer!!

Thank you, Lin, for this NON-ANSWER, answer. It means we are on our own. You got a problem? Go find your own answer!!

That is about it. However have you completed the Yahoo migration that xfinity are doing? Most of the folk that have landed here complaining about their Comcast mail ignored the invitation to move and had their Comcast mail accounts closed.

See https://help.yahoo.com/kb/SLN36803.html and https://www.xfinity.com/support/articles/yahoo-email-migration-overview

Outlook works great; all my accounts work, so I say goodbye to Thunderbird

Thank you, Lin, for this NON-ANSWER, answer. It means we are on our own. You got a problem? Go find your own answer!!

Sorry if you took my comment badly. I don't have a solution for you, but I just wanted to stress the point that there ain't nobody here but us chickens. We are users trying to help others using our own time, effort, and experience.

Good luck with Outlook and trying to call Microsoft Support when you have a problem.