There have been recent problems with Webmail.
It has been found to be related to newer versions of Internet Explorer (V11).
One noticeable problem is only being able to create messages in plain text.
Comcast Support has provided a fix -
While you are at webmail site - select Tools in the menu, then Compatibility View Settings
It should show you can add Comcast.net
Log out of Webmail and back in.
That should fix problems with Webmail.
Thank you for sharing your experience and insight to the community.
The community appreciate it!