This URL may help: https://www.xfinity.com/support/articles/third-party-email-access you need a unique password for use in an email client,

This URL may help: https://www.xfinity.com/support/articles/third-party-email-access you need a unique password for use in an email client,

Where does it say you need a 'unique password' for a mail client? That URL says you need to enable access by mail apps, but the password for the app is the Xfinity account password.

To the OP: when you changed the password, did you remove the old one from Saved Passwords in Settings, restart TB, and enter the new password when prompted?

Thanks for clarifying, @sfhowes. My error.

I had the same problem. After changing password for xfinity, I could not get any email updates, even after changing it in TB. my solution was to delete the account and reinstall it using the autosetup. After typing in the new password and testing, the connection tested good and all my emails returned. I just hope I don't have to do this everytime I change my password.

I have the same problem. After deleting my Google and Xfinity emails from Thunderbird, then closing and reopening Thunderbird, I'm still getting this error from Google:

400. That’s an error.

The server cannot process the request because it is malformed. It should not be retried. That’s all we know.

I can't reconnect to Xfinity at all. The 3rd party box is checked, but when Thunderbird tries to connect, it looks like it's autofilling and submitting a password on my behalf, faster than I can grab it and change it, even though I deleted the saved password and removed that account.