Have to reset passwords after a Restart for Windows update.

Update 9/18/2026 - I have reset the passwords and rebooted each time, to no avail, Still get the same bogus error message that the server has reject the password. Now it will not down load! I can access all mail on the Comcast server and have NO issues with my mail on my iPhone and iPad. Everything points to Thunderbird.

If I uninstall Thunderbird and reinstall a new download, can I use my saved profiles to get everything, saved data and e-mails, to restore it back to normal?

I have the same general setup as you on several computers - Comcast, Windows 10 and 11 - and I've never had any such problems, so that suggests some unusual factor on your computer.

First thing I'd check is to confirm my 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: OAuth2

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

These are the same as what you find at their help page:

https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email

EXCEPT that they make no mention of OAuth2. I think they silently introduced OAuth2 a couple of years ago but didn't bother to tell anybody. The old, less-secure Normal Password authentication method seems to still work.

What Anti-Virus, other security software do you use, if any? Many of them have a bad habit of grabbing onto files an not letting go, which might result in symptoms like yours. The fix for that would be to create an exception in the AV for your Profile folder.

Lin, Thanks for the tips. I have done all of that, to no avail. This morning everything was back to normal, all by itself! Well, for the moment anyway🤞

I will suggest you probably had an antivirus issue. A product not on your iDevices probably so they are unaffected and using a web browser to get mail simply confirms you can access a webpage it does nothing to suggest relevant .. I read you issues and unlike you I thought everything pointed to the antivirus really, not Thunderbird.

It is most often a software firewall that causes the issue and when it is updated when the antivirus calls home updates after a few days things "just start working again"

Thanks Matt.