Password

You should first verify your server settings. Here are my working Comcast settings:

IMAP (Incoming): 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 OR OAuth2

SMTP (Outgoing): SMTP Server Name: smtp.comcast.net Port: 465 Connection Security: SSL/TLS Authentication method: Normal Password OR OAuth2 User Name: <my email address>

I use IMAP but if your incoming server is POP3, you would use this:

POP3 (Incoming): Incoming Server Type: POP Mail Server Incoming Server Name: pop3.comcast.net Port: 995 User Name: <email address> Connection Security: SSL/TLS Authentication method: Normal Password (or OAuth2?)

These are the same as what Comcast recommends (see https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email) except they don't mention using OAuth2 as the Authentication Method. OAuth2 is better, but the older, less-secure Normal Password method may still work.

To make OAuth2 work properly in Thunderbird you must make sure that cookies are allowed (see <Settings | Privacy & Security | Web Content | Accept Cookies from Sites>.) You should also delete any existing Comcast entries in Saved Passwords (see <Settings | Privacy & Security | Passwords | Saved Passwords>.) Then, restart Thunderbird. You will be prompted for your credentials and you should be authenticated.

I haven't changed any of the settings but was using a different computer to access Thunderbird for a couple of weeks ( a home computer) but I didn't change anything there either. Thanks.