Try this:

- Delete your saved Comcast/Xfinity password from Thunderbird's Saved Passwords. They can be found in <Settings | Privacy & Security | Passwords | Saved Passwords button>. You will find at least two entries, one for the IMAP server, one for SMTP.

- Check for saved cookies. They can be seen in <Settings | Privacy & Security | Web Content | Show Cookies button>. There may not be any there, but if there are, delete them.

Now restart Thunderbird. When it checks for mail and when you send mail, you will be prompted for your password.

This usually works, but not always. Please report back with your results.

Thanks, Lin. I just followed your directions (above) exactly. Unfortunately, I still have the same error. Of course, I entered the same password, which is still correct for online login, correctly.

Any other suggestions? Thank you.

Earlier this Sunday morning, Thunderbird began receiving Comcast emails again as usual. Practically, I did nothing to resolve the problem. Thus, whatever happened fixed itself. Ain't modern software wonderfully aggravating?

I'm thinking Comcast was having technical difficulties, not that they would be likely to admit it. You weren't the only one having unexplainable logon difficulties - I saw at least two others yesterday. I'm glad your problem resolved itself - I was out of ideas. Hope theirs did, too.

Thanks, Lin. I too suspected a problem on Comcast's end.