Multi-Domain
The Multi-Domain cert may also be called a Multi-Domain/SAN certificate depending on which CA you are considering. For example, Comodo offers an EV Multi-Domain SSL which provides you with the advantage of having multiple domains with the green address bar and full business validation, ideal for larger companies or organization needing to secure multiple domains and subdomains on one certificate. The basic product comes with three Fully Qualified Domain Names by default, it can be added up to 250 fully qualified domain names with additional SAN purchase.
UC Certificate
The UCC or UC Certificate (Unified Communications Certificate), is a very specialized type of SSL/TLS product. Like all of Comodo's products it can be used with any server platform, but it has been specially designed to work within the Microsoft Exchange and Office Communications server environments. These servers have specialized features, tools and options that the UCC is configured to work with and in. For example, with the Microsoft Exchange, the autodiscover feature will work with the Comodo UCC product. It does not work with the other SSL/TLS products without significant workarounds which are both time consuming as well as potentially problematic.
The UC certificate and Wildcard SSL offer protection for main domains and subdomains. The UCC like the Multi-Domain SSL can support up to 250 main domains and subdomains on the same certificate.
Wildcard SSL
There are two big differences between the UC certificate and Wildcard SSL. The Wildcard is only able to protect one domain and that main domain's subdomains. The UCC can secure both main domains and subdomains up to 100 entries. This is an important distinction to keep in mind.
The other major difference is that the UC certificate and Wildcard SSL are not recognized the same by the Microsoft Exchange and Office Communications servers as well as browsers and devices. Mobile devices before Windows Mobile 6 will not recognize Wildcard certs, but they will recognize the UCC.
Security is also enhanced with the use of the UCC as there is no "wildcard" component on the certificate. This means that a site cannot be set up to mimic an authentic site using the wildcard certificate. While this is rare, it can and does occasionally occur if the private key information is not secure or if there is a breach on a server. It is possible, and perhaps necessary for some specific situations, to combine the UC certificate and Wildcard SSL. If this is the case, Comodo UCC OV Wildcard SSL you may consider.
The UC certificate and Wildcard SSL are not available at the extended validation level. This may be a consideration for some websites and this can be another discussion to have with our sales team for the most cost-effective option.