How Many Certificates?
Customers who do not have dedicated servers, you would need separate TLS certificates for each of the following scenarios.
Web Site Hosting
You will need one TLS certificate for each secure web site that you wish to have hosted. This certificate will be for either "domain.com" or "www.domain.com" — your choice. Generally, a single TLS certificate will not match both names.
Private Labeling of WebMail
If you have Private Labeled WebMail and wish to brand the domain name shown in the browser for TLS connections, then you will need a TLS certificate for that "secure private labeled domain name".
Note that you can use the SAME "secure private labeled domain name" for:
I.e., there is no need to get separate domains and certificates for all of these services. You can use insecure "vanity domain names" for access. For example:
Private Labeling of Email
If you have Private Labeling and a dedicated email server and wish to have your users use your secure domain for access to secure POP, IMAP, and/or SMTP services, then you will need to pick another domain name, such as "mail.domain.com", for this and obtain another TLS certificate for it.
Note: Private labeling of TLS connections to email services is not available to customers using shared email hosting servers.
Dedicated Server Customers
Dedicated server customers may have their email and web hosting services on the same server. The can use the same domain name that they are using for secure web site hosting for secure private labeled email access (there is no need for separate domain names in this case).