I'm runnng Thunderbird on Ubuntu 18.04 and encountered this issue starting on Friday, November 30, 2018. Prior to that, Thunderbird worked fine. I've been in contact with Comcast Support over two hours on this at various times. I even brought up using the imap.ge.xfinity.com server, but agents seemed puzzled by that. As well, they seemed puzzled about using other than Outlook. BTW, using imap.ge.xfinity.com server works, but I didn't like the idea of not having acertificat for port 143. At any rate, after working with support with several attempts at completng the server, port, and authentation. I concluded that it is a Thunderbird-Ubuntu issue. I confirmed by setting up an Ubuntu VM on a Windows host and encountered the same issues as with my Ubuntu machine. I chose to install libnss-resolve. Installing libnss-resolve fixed the problem. I would like to see the bug to determine why the problem occurred when it did. I'll check further.
Thanks for the solution!
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