Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
How do you normally access your comcast mail, through the stamp or mac mail app?
Also, can you find your version of osx, heres how. Click the apple sign at the top left of your screen, then click about this mac. And then where it says version, send that to me as a reply.
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.