A Unified Communications Certificate (UCC) is a type of multi domain SSL certificate. A UCC lists a main Fully Qualified Domain Name (FQDN) for the certificate, with every additional domain is listed as a subjectAltName (SAN). This is different from a true multi domain certificate, where every single domain is listed as a subjectAltName (SAN) and there is no main domain name.
Why purchase a UCC SSL Certificate?
It is this distinction that makes a UCC compatible with Microsoft Exchange Server, Live Communications Server and Microsoft Office Communications Server environments. Both servers can have several functions – both internal and external – assigned to different subdomains, all of which can be on a single IP address. The device will look for the main domain name on the certificate, and then look for the appended subdomains. A true multi domain certificate is not able to be used as there is no main domain name to look for on the certificate, it displays each domain as a SAN on the certificate with no main domain name.
A UCC certificate can also be used for payment gateways, Android devices, Skype servers however is most commonly used for autodiscover, which does not work with the other SSL/TLS products without significant workarounds which are both time consuming as well as potentially problematic. Autodiscover is commonly used in the Exchange platform as it greatly eases administration.