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From the EnTrust certificate site:
A SAN or subject alternative name is a structured way to indicate all of the domain names and IP addresses that are secured by the certificate. Included on the short list of items that are considered a SAN are subdomains and IP addresses.
When additional actions on a website need to be secured, the SANs need to be included on an SSL/TLS certificate so that the DNS server can resolve the IP address to the domain name. This will give the page the HTTPS indicator that meets browser guidelines and that give visitors confidence to transact on your website.
This is what the SANs would like in the certificate details:
SAN 1: DNS Name=example.com
SAN 2: DNS Name=
www.example.com
SAN 3: DNS Name=example.net
SAN 4: DNS Name=mail.example.com
SAN 5: DNS Name=support.example.com
SAN 6: DNS Name=example2.com
SAN 7: IP Address=93.184.216.34
SAN 8: IP Address= 2606:2800:220:1:248:1893:25c8:1946
The SANs information appears in the SSL/TLS certificate details that can be viewed by clicking on the locked padlock in the address bar of most web browsers.
This screen captures how the Subject Alternative Name field displays the various SANs in certificate details
EV Multi-domain or
UC SSL/TLS certificates are sometimes used in environments where IT administrators need to frequently add, change, or remove domains. Having the ability to secure multiple names across different domains on a single certificate provides flexibility, efficiencies and cost savings.
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In summary: This is the era of virtualization and cloud data pools. The days of an entire site being run off a single discreet physical server went away over a decade ago. Using multiple names in a certificate is common practice when multiple secured services are required to verify data points - like mailing addresses, e-commerce, hooks into shipping scalars, regulatory databases, etc.