I tried to get/download my emails a couple days ago and am not able to do so. I use Thunderbird for my emails on my Windows 10 system. On 12/26 Windows updated itself to Win 10 version 1709 . I didn't try to download my emails until after the new Xfinity email "wrapper" appeared.
When I try to download emails each step of the process as shown by Thunderbird is much slower as if there is a problem. There is a three step process with the last step being "Checking inbox for new messages". The program hangs there for many seconds and then posts a simple message "the are no messages to download" or something along those lines. This last message pops up for a second or two and disappears. There are definitely messages available for download as I've downloaded new messages for 4 or 5 days now. It appears that Thunderbird can at least get enough of a handshake to connect to Xfinity and send my password.
I think the issue relates to my Windows 10 upgrade to the "1709" version installed around 12/27.
Also, I have a Samsung cell phone (Android) that accesses my Comcast.net email and that seems to be working perfectly.
I was upgraded to the new version of webmail [Appsuite] today and had problems downloading email into Thunderbird. Once I changed my settings in Thunderbird, I had no problems downloading my mail. The settings in webmail show to use port 993, but that didn't work for me, so I changed back to port 995. However, I had to change the incoming server from imap.comcast.net to imap.email.comcast.net in order to get my mail to download. You might want to try that.