Thunderbird does not support two factor authentication. So I would be guessing you need to use an application password supplied by comcast.

I can't find anything on their web site about application passwords, but this outlook support topic contains instructions. I have no idea how current they might be. https://answers.microsoft.com/en-us/outlook_com/forum/all/trying-to-add-a-comcastnet-email-account-to-the/fd90760a-ee8c-40fc-8a18-199209667820

Try with OAuth2 authentication and enter the account password in the OAuth prompt:

https://support.mozilla.org/en-US/questions/1442111

Sorry, I did not completely understand your settings and creating a second account from the first. How do you use the second account. My settings did not work. I finally used manual settings but I am not sure what the computer did. I thought the second account should have a different name but used the same name as the first.

If you already have an IMAP account entered in TB, try these settings, and if not, add the account and use the manual config.:

Incoming Mail Server: imap.comcast.net Port: 993 Connection Security: SSL/TLS Authentication Method: OAuth2 User name : email address.

Outgoing Mail Server: smtp.comcast.net Port: 587 Connection Security: STARTTLS Authentication Method: OAuth2 User name : email address.

Make sure 3rd-party access is enabled:

https://www.xfinity.com/support/articles/third-party-email-access

THAT DID NOT WORK. I could not click done. I got a message that the in server already existed.

Just a reminder. I don't have a smart phone and I can't read or text messages. Also, I don't know how to get Comcast to send email with s pass code in it, Currently, VISA sends an email passcode to my bank so I can access my credit card information. I don't really know how this works. my bank dose not maintain the web page. I have to call VISA.

Open Account Settings. Is the account already listed in the left pane? If it is, go ahead and enter the recommended settings.

I was able to down load some messages this morning. When I tried to send a message it asked me for some ID but did not allow me to input any information. I tried to copy and paste the message using snip but it did not work. The only passcode I get is from VISA to access my credit card account at my bank. I don't think this email passcode would work to access my email files at comcast/

Screen shot Attached. I was able to send message VIA Xfinity email and read the received message with Thunder bird.

Do you have a VPN or some kind of web server running in the background? That might explain the localhost error.

Yes McAfee rums VPN. I am still reading new messages on Thunderbird. I tried to send a screen shot of one of the messages but did knot know if you received it.

I received a copy of my screen shot on Thunderbird. Also, Microsoft started sending files to the cloud without my permission. I don't know how to stop this.

Disable the VPN while using email. You can probably stop files going to the cloud by adjusting your OneDrive settings.

I turner off VPN s couple of hours ago. I tried to send messages from Thunderbird. I get the same error message. I don't really know if I use the cloud. I looked at the settings but did not find a way to turn it off. I do not log onto Microsoft when I start my computer so I may not be using the cloud. I click on the cloud Icon to speed up the delivery of a passcode for my bank's credit card account. The error message mentioned the settings for imap.comcast.net but my computer only shows the settings for SMTP.

I have had my Comcast email within TB for years. I just today changed the name and now I cannot receive or send emails from the new Comcast email within TB. Comcast/Xfinity has verified that my current settings within both TB and my Comcast account are correct. I have the 115.9.0 version. I just keep getting the same Alert stating error code 1014. Can anyone solve this ?

Sfhowers helped me get started on Thunderbird. I can down load messages from most users except comcast. Also, I can't send messages from Thunderbird. I get this message when I log onto Thunderbird: Enter Credentials for your email address (i did not print my email address) on imap.comcast.net. The box below seemed to be working but I do not know what web link to input. Comcast gave me a passcode to get started on their webpage. After logging on I clicked the button remember my device. Jerry

I still can't send messages from Thunderbird. I am getting a new question. Enter Credentials for my email address on imap.comcast.net I don't know how to enter this information. Also, I do not have a smart phone. Downloading email from other users is working except for Xfinity. I downloaded a lot of information about changing from POP3 to imap account. Jerry