Mail account not showing in Internet Accounts screen.

I have three mail accounts iCloud, Gmail and Comcast. Only two of the accounts show in my Internet Accounts screen. The third one (Comcast) does not show. The Comcast account appears to be working. When I try to reinstall the account I get a message the the account already exists and because is doesn't show I cannot delete it and reinstall. I am running OS X El Capitan on my iMac. Any suggestions would be appreciated.

John