A multi-domain SSL certificate, also called a SAN certificate or a UCC certificate, secures several different domain names with a single certificate. Instead of installing one certificate per domain, you install one certificate that lists every domain you want covered.
What Makes It Different From a Normal Certificate
A standard SSL certificate covers one domain name (and optionally its www version). A multi-domain certificate uses a field called the Subject Alternative Name (SAN) to list multiple, unrelated domain names on the same certificate, for example yourbusiness.com, yourbusiness.co.ke, and yourotherbrand.com all at once.
"SAN" refers to that technical field, and "UCC" (Unified Communications Certificate) is an older name for the same type of certificate, originally used for Microsoft Exchange and Office Communications environments. Today the terms are used interchangeably for any certificate covering multiple unrelated domains.
When You Might Need One
- You run several separate brands or businesses, each with its own domain, hosted on the same account.
- You have a main domain plus a handful of addon domains that don't share a common base name, so a wildcard certificate (which only covers subdomains of one domain) won't cover them.
- You want one certificate to manage and renew instead of tracking renewal dates for several separate certificates.
If all your domains are subdomains of the same base domain (for example shop.yourbusiness.com and blog.yourbusiness.com), a wildcard certificate is usually the simpler and cheaper choice. A multi-domain certificate is for when the domains themselves are different, not just different subdomains of one domain.
Most small businesses with a single website and a single domain don't need a multi-domain certificate. AutoSSL already issues and renews a free certificate for your domain and its common variations automatically. Only consider a multi-domain certificate if you're genuinely managing multiple separate domains that need to share one certificate.
SAN/UCC vs Wildcard vs Separate Certificates
- Separate certificates: one certificate per domain. Simple, but more certificates to track and renew.
- Wildcard certificate: one certificate that covers one domain and all of its subdomains (*.yourbusiness.com). Doesn't help if your domains are entirely different names.
- Multi-domain (SAN/UCC) certificate: one certificate listing several unrelated domain names. Best when you manage multiple distinct domains and want a single certificate to renew.
How to Get and Install One
- Decide on the full list of domain names the certificate needs to cover, since most providers charge based on how many domains (or "SAN slots") are included.
- Generate a Certificate Signing Request (CSR) for the primary domain, the same way you would for any paid certificate.
- Purchase the multi-domain certificate from a certificate authority, providing the additional domain names to be added as SAN entries.
- Install the issued certificate the same way you would install any other paid SSL certificate.
Each additional domain on the certificate still needs its own A record or hosting pointed correctly, and you'll need to update the certificate (and usually pay an additional fee) if you later add another domain to the list.
For the CSR and installation steps in detail, see How to Generate a CSR for Your SSL Certificate and How to Install a Paid SSL Certificate on Your Website.