Hosting multiple SSL-enabled sites on a single server typically requires a unique IP address per site, but a certificate with Subject Alternative Names can solve this problem. Microsoft IIS 6, 7 and Apache are both able to Virtual Host HTTPS sites using Unified Communications SSL certificate, also known as SAN certificates.
Using a SAN certificate saves the hassle and time involved in configuring multiple IP addresses on Exchange 2007 server.
When browsers connect to server using https, they check to make sure SSL certificate matches the domain name in the address bar.
There are three ways for browsers to find a match:
Comparing the Server Name it connects to, with the Common Name in the Server certificate, is a common way browses match the domain name typed in the address bar.
It is safe to assume that all SSL clients support exact common name matching.
If an SSL certificate has a Subject Alternative Name (SAN) field, then SSL clients are supposed to ignore the common name value andseek a match in the SAN list.
The SAN attribute is available with all Verisign certificatesData Sheet