What Is a ‘Subject Alternative Name’ SSL Certificate – And Why Does It Matter?

A Subject Alternative Name (SAN) is a certificate that secures multiple domain names, subdomains, or IP addresses. It is a way of telling your web browser that one certificate works for multiple sites.

Some people call them Unified Communications Certificates (UCC), multi-domain certificates, or Exchange certificates. Same thing, different names. They all do the job of securing multiple domains under one certificate.

A common mistake is assuming CN and SAN are the same thing. They’re not.

• The Common Name is the primary domain the certificate protects.

• The SAN field lists all the additional domains or subdomains also covered by the certificate.

The biggest advantage of SAN certificates? Simplicity. It improves SSL certificate management by enhancing basic functions.

Instead of tracking dozens of separate certificates across your environment, you can consolidate them under one certificate. That means fewer renewals, less manual tracking, and lower risk of missed expirations—helping your team avoid unplanned outages and compliance issues.

This is a game-changer for big companies with sprawling digital footprints and keeps security policies consistent across all domains.

It also supports scalability for organizations launching new digital services or consolidating domains after mergers and acquisitions. You can simply add new domains to the SAN list during renewal or reissue, rather than managing separate certificates. 

How SAN Works in SSL Certificates Management

When a web browser connects to a site, it checks the SSL certificate to ensure the domain matches one of the names listed in the SAN field. 

Imagine a company, ExampleCorp, that owns multiple websites and services under different domains:

1. examplecorp.com (Main website)
2. www.examplecorp.com (Common subdomain)
3. shop.examplecorp.com (E-commerce portal)
4. support.examplecorp.com (Customer support platform)
5. examplecorp.net (Alternative domain for international users)

Instead of buying separate SSL certificates for each domain, ExampleCorp can obtain a single SAN-enabled certificate that covers all these domains. When users visit any of these sites, their browser checks if the domain is in the SAN and confirms a secure, encrypted connection.

This improves user trust: visitors are always interacting with secured domains, which is especially important for e-commerce or customer service portals handling sensitive data. Browsers display security indicators like padlocks more consistently across all subdomains, reducing user confusion and abandonment.

It also streamlines compliance efforts. Many data privacy regulations and industry standards require encryption for data in transit. By covering multiple domains under one SAN certificate, organizations can meet these requirements more easily and demonstrate consistent security controls during audits. This is particularly helpful for regulated industries that operate a mix of public-facing internal applications across different environments. 

Here are other common use cases well suited to SAN certificates:

• Securing www and non-www versions of a domain
• Mail servers with multiple domains
• Load balanced web servers
• Multiple internal hostnames/IPs

Note that SAN is an extension within the X.509 certificate. X.509 is the standard format for public key certificates used in SSL/TLS encryption. So, all SAN certificates are X.509 certificates, but not all X.509 certificates have SAN extensions.

How to Obtain and Manage a SAN SSL Certificate

The process of obtaining and managing a SAN certificate can be grouped into 4 steps; they include: 

Step 1: Choose a CA

Once you’ve figured out the domains or subdomains you want to cover with a SAN certificate, the first task is to pick a trusted Certificate Authority (CA) that offers SAN certificates.

Before you settle on a CA, make sure to check the pricing, validation requirements, and the number of SAN entries they support.

Step 2: Submit a CSR

Now, it’s time to submit your Certificate Signing Request (CSR) to the CA. The CSR should include your primary domain (Common Name) and any other domains or subdomains you want to secure.

You can easily generate a CSR using OpenSSL, a web-based CSR generator, or control panels like cPanel and Plesk. After creating your CSR, submit it to your chosen CA. To do this 

• First, purchase a SAN SSL certificate that supports multiple domains, and complete any account registration steps if needed.
• Then, log into the CA’s portal, go to the SSL certificate section, and choose the option to submit your CSR. You can either upload the CSR file (example.csr) or paste the content into the provided text editor.

Step 3: CA ownership verification

The next step is for the CA to verify you own the domains. They do this through three main validation methods:

• Email Validation: The CA sends a verification email to an admin email address.
• DNS Validation: You add a TXT record to your domain’s DNS settings.
• File-Based Validation: You upload a specific file to your site’s root directory.

Once the CA approves the CSR, they’ll issue the SAN certificate, which usually includes the primary certificate (example.crt) and an intermediate CA bundle (ca-bundle.crt).

Step 4: Implement on web servers

Now, it’s time to install the SAN certificate on your servers. For Apache, this involves uploading the certificates, editing the ssl.conf file, and restarting Apache. The process is similar for Nginx. But if you’re using cPanel or Plesk, just go to the SSL/TLS settings, upload the certificate, and assign it to the domains.

To verify the installation, you can use online tools like SSL Labs or Why No Padlock.

Next Steps: Keep Your SAN Certificates Working for You

Buying and installing SAN certificates is just the beginning. To truly protect your environment, and get the most value, you need to manage them consistently and securely.

Here’s how to stay ahead:

• Evaluate your SSL/TLS certificate strategy – Make sure it aligns with your current domain structure and security policies.

• Automate SAN certificate lifecycle management – Tools like Keyfactor Command help you track expirations, send alerts, and avoid costly outages.

• Use fresh CSRs during renewal – This keeps cryptographic material up to date and reduces the risk of compromise.

• Review and update domain entries regularly – Remove unused domains to tighten security and ensure certificates reflect your current infrastructure.

Staying proactive prevents unexpected lapses that could impact multiple services at once. With the right strategy, you’ll turn your SAN certificates into a strength, not a vulnerability.