Some years ago, I cannot recall, Go Daddy along with many other SSL certificate providers stopped supporting Subject Alt Names (SANs) that had the local FQDN of your mail server in it. Example: mailserver.domain.local. Email servers today need to have a UCC certificate. There are many places where you can obtain free certificates , such as STARTSLL.com. As of late, Go Daddy was instumental in getting some StartSSL IP address black listed. This issue has been resolved and they are back at it. Obviously, free vs 400/year is a good deal.