Gmail Connectivity

I have been using Gmail for all of my email addresses for years.  Recently all email from my comcast account via gmail has been blocked by many servers including comcast accounts.  I have no issues receiving emails, just sending them.

My current settings in Gmail has the smtp server as mx2.mxge.comcast.net.  I have attempted several times to set it to smtp.comcast.net, using both my email and just my username as the "username" and even copied and pasted my email address (as well as typing it in).  I am allowing 3rd party access in the mail security settings.  When I attempt to connect to the server via Gmail I get the error message "Couldn't reach server.  Please double-check the server and port number.  

Help!