Can't help if Comcast do not have a clue. I do mean that seriously. They are next to useless in providing anything resembling email support

This is the information on their own web site. https://www.xfinity.com/support/articles/update-pop3-110-995

It is for xfinity. So I assume that is what you have.

It says your account settings... that will be in server setting for the existing account in the account list should be set to port 995 and connection security should be set to SSL. I am assuming the Thunderbird setting of SSL/TLS will work, as that is what they show in the image.

Incoming Server (Name "(pop3) mail.comcast.net:995 SSL/TLS 

should be what appears in your troubleshooting information that you posted.

You might want to read the information in the questions and answer part at the bottom and then ask Comcast why they treated you so poorly as to not offer you correct advice. You are their customer, so they are not guessing like I am.

Comcast Tier 2 cannot fix the problem. Tried to "Remove Account" in Account Actions, but could not invoke that action. Had the gall to blame Mozilla for not knowing how to overcome Comcast Tier 1's failure to follow its own published protocol for changing server settings on Thunderbird. I guess I will have to change emails or change email clients. Thanks for your quick response.

12times said

Comcast Tier 2 cannot fix the problem. Tried to "Remove Account" in Account Actions, but could not invoke that action. Had the gall to blame Mozilla for not knowing how to overcome Comcast Tier 1's failure to follow its own published protocol for changing server settings on Thunderbird. I guess I will have to change emails or change email clients. Thanks for your quick response.

Personally I have doubt Comcast could move a small branch off the front path to clear a blockage, let alone actually offer anything remotely like support. But perhaps I am biased, never having dealt personally with their brand of cookie cutter support. I only get to see the often disastrous results from their customers in this forum.

However, what part of changing your settings is causing trouble. If accessing the account settings gets an error about an account already existing, that can be cleared simply by changing the account name in the box the cursor is blinking in. (This is an account name, nothing to do with your settings, so it could luckyday. But usually I suggest you just add a 1 onto what is there and clicking Ok.)

Once you have renamed the account restart Thunderbird. Then we will have to work out exactly what duplicate and probably non working account you have added in your flurry of attempts to fix your problem by adding the account again to Thunderbird is the excess one.

As suggested, clicked on "Tools", "Account Settings," and changed "Account Name" by adding a "1" in the local-part of the email address, which constitutes the Account Name. Then clicked on Server Settings under the old account name (without a "1" in the local-part), which I was able to see (for the first time since the Comcast "Support Team" intervened) without an error message to the effect that the account already exists. Also clicked on "Outgoing Server (SMTP)", which I was able to see, again for the first time without the error message. Each set of server settings (incoming and outgoing) for the old account name matched the server settings for "account3" in the Troubleshooting Information under "Mail and News Accounts". The other account ("account1") has no server settings.

12times said

the server settings for "account3" in the Troubleshooting Information under "Mail and News Accounts". The other account ("account1") has no server settings.

The port should show as 995. Is that correct?

Yes, the port shows 995.

Can you please post the account details from the troubleshooting information again?

You might also want to try restarting Thunderbird and your computer in safe mode to be sure it is not other software on your device that is interfering and causing the problem.

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Attached is a screenshot of the Troubleshooting Information. After restarting Thunderbird in regular mode, incoming and outgoing messages appear to be working properly. All suspended messages have been restored.

I will consider this closed unless you have more issues. Those settings should certainly work.

Thank you for your support, Matt. The issue is closed.