reply to Downers Grov
Just found this post from a Comcast employee in the Email Help area of the Comcast Help and Support Forums (»forums.comcast.com/t5/E-Mail-and···#M220061 ):
From: aorapal (Official Employee)1-04-2013 2:06 PM - edited 1-04-2013 2:07 PMwe had an issue with our DNS servers (for comcast.net) a couple of hours ago. That issue has since been resolved and smtp.comcast.net (and all other comcast.net urls) should be resolving correctly now.