If you're using Comcast@Home to check your e-mail outside of the Comcast network, then you need to sign up for netmail on the @Home webpage when you're on their network, and then you can check netmail.home.com for your e-mail.
If you're inside of their network right now, you can just check mail.<dns> ... If your computer was setup by a @Home person then they should have added the rest of the dns to your "automatically append DNS suffixes" ... If not, it is the same DNS suffix that you get when you look up your IP address in the DNS ... So for example, if your DNS is abc12.xyzxyz1.nj.home.com then your mail server is mail.xyzxyz1.nj.home.com ... if the dns is automatically appended then its just "mail".