Hi:
Per your description, you got services not available error when you use MOC from external.
1. Like Deli Pro said you can use the internal certificates for the MOC from the external. But you should have configured the proper Authentication Certificates on the edge server firstly. You can comprehend clearly how to configure those refer to below links:
http://technet.microsoft.com/en-us/library/dd425344(office.13).aspx
http://technet.microsoft.com/en-us/library/dd425107(office.13).aspx
http://technet.microsoft.com/en-us/library/dd441270(office.13).aspx
http://technet.microsoft.com/en-us/library/dd441368(office.13).aspx
According to the links you can check the configurations of your servers are right or not.
2. Other side, you also should check the DNS Requirements for External User Access and DNS requirements for Automatic Client Sign-in firstly. you can refer to below links:
http://technet.microsoft.com/en-us/library/dd425138(office.13).aspx
http://technet.microsoft.com/en-us/library/dd425235(office.13).aspx
Hope this helpful!
Regards!
