There appears to be an error in your setup. Possibly, if you post screenshots of your incoming server settings pane and the SMTP server settings pane, some suggestions will come forth. Localhost is not a server.

Same thing started happening to me a few days ago. It worked when I checked before going to bed, but not in the morning when I got up. Connection is refused by something somewhere, and the program is what is trying to connect to 'localhost', not me. The automatic set up has been altered somehow.

My symptom: Unable to connect The connection was refused when attempting to contact localhost.

The site could be temporarily unavailable or too busy. Try again in a few moments. If you are unable to load any pages, check your computer’s network connection. If your computer or network is protected by a firewall or proxy, make sure that Thunderbird is permitted to access the web. If you are trying to load a local network page, please check that Thunderbird has been granted Local Network permissions in the macOS Privacy & Security settings.

I’m on a Mac, but only recently. Years of PC user experience. My firewall is off. Tried changing IMAP port from 993 to 80 as advised on youtube. No error, but nothing downloaded. Can get to my email on comcast.net directly, just not via Thunderbird. Afraid to try too much else for fear of screwing things up royally. If you can help, please give clear, step-by-step basic guidance. (I retired in 1998, so my computer knowledge is pretty outdated.)

It sounds like some program may have inserted itself between Thunderbird and the Internet, intercepting traffic to certain ports and possibly redirecting it to another port, in this case localhost. It could be an anti-virus program... or it could be malware. Do you use an Antivirus or other "security" program? Do you have Thunderbird set to use a proxy (see < Settings | General | Network & Disk Space | Connection > - click the Settings button and see if it's set to use a Proxy. Normally "Use system proxy settings" is the best choice.

By the way, it's best to start your own new topic rather than add to an old, possibly already-resolved one.

Thank you Lin. “Use system proxy settings” is checked MAC System Settings- Network - Firewall is turned off

Perhaps this will help? (I expect the red asterisks may be significant???)

Trying to set up Email (Local Folders - Email - [Enter Full Name and Email address] Press “Continue” - get Mozilla Account Hub screen, which says “Configuration found in Mozilla ISPDB” IMAP checked - Press “Continue” - get “Error Creating Account” - click "Show More" - get “Incoming eerver already exists” {I don’t know how to respond to that}

Incoming server settings: imap.comcast.net (check mark) Port: (red asterisk) 993. (check mark) Connection security: SSL/TLS Authentication method: OAuth2 Username (red asterisk) {My email address entered} (check mark)

Outgoing server settings smtp.comcast.net Port (red asterisk) 465 (check) Connection security: SSL/TLS Authentication method:OAuth2 Username (red asterisk) {My email address entered} (check mark)

Clicking “Test” on the Outgoing server settings screen produces” (check) :The following settings were found by probing the given server” BUT the settings shown are all identical to those above: Outgoing server settings smtp.comcast.net Port (red asterisk) 465 (check) Connection security: SSL/TLS Authentication method:OAuth2 Username (red asterisk) {My email address entered} (check mark)

Here are my Comcast settings:

Incoming Server Type: IMAP Mail Server Incoming Server Name: imap.comcast.net Port: 993 User Name: <my email address> Connection Security: SSL/TLS Authentication method: Normal Password

SMTP Server Name: smtp.comcast.net Port: 465 Connection Security: SSL/TLS Authentication method: Normal password User Name: <my email address>

The difference I see is that you are trying to use OAuth and I'm not. I'm not sure Xfinity/Comcast even used Oauth. So, try my settings.

A confusion arises because, as you may know, Comcast is working to pass off their email service to Yahoo. I've gotten conflicting reports of when and how this is going to happen, but it hasn't happened to me yet. Yahoo DOES use Oauth, but unless they have forced you to transition, I think my old tried-and-true settings may work until they do.