Change the outgoing server port to 587, but don't check SSL...
Run mail.
Select the 'Mail' menu (next to the Apple symbol).
Select 'Preferences'.
Click 'Accounts' in the window which opened.
Select the comcast account.
Click 'Advanced'.
Change the port number from 110 or 995, to 587. Don't check SSL.
Close the window, Click 'Save' when prompted.
