Multi Domain Certificate for Exchange
To secure an Exchange Mail server use of a multi domain certificate is recommended. This counts for Exchange 2007 and higher.
The multi domain certificate is also called a UCC (Unified Communication Certificate) certificate. In this certificate, several domain names have been included, thus allowing the use of the auto-discover and web mail domains as well as the internal domain name in the same certificate.
In principle it is also possible to use a certificate for a single domain. In that case, the clients need to be set manually, and use cannot be made of an internal server name or auto-discover functionality (which automates the configuration of clients). Use of a UCC certificate enables this.
Note: Using internal domains in a multi domain certificate will no longer be allowed after October 2015.