Xfinity email accounts stopped working with Thunderbird

I noticed sometime today I stopped receiving emails to my Thunderbird email client on my pc. I removed my main email account from Thunderbird, and can't add it back, but I have three other email accounts still added to Thunderbird which can't receive or send emails.

I'm posting a screenshot of the error message I get when trying to send an email from one of my Xfinity email accounts through Thunderbird. Sending and receiving emails is working normally through the Xfinity website.