Don't know if it is related or not, but about an hour ago I was not able to access the Comcast Homepage. The URL I was using is below
http://xfinity.comcast.net/
I also noticed that the redirect that was in place to go from »
www.comcast.net to »
xfinity.comcast.net/ was also not working.
However, I am now able to open both pages without any problems.
Depending on what caused their main page to not open may have effected mail delivery, if you were trying to do it on Comcast's webpage (not using an external program like Outlook or Thunderbird).
So, I would see if you can even get to their homepage. If not, give it some time, and try again.
--Brian