A CNAME (Canonical Name) record cannot coexist with any other DNS records that use the same hostname.

This means that if a hostname has a CNAME record, no other DNS record types can be created for that same name, including:

• A records
  
   
• AAAA records
  
   
• MX records
  
   
• TXT records
  
   
• SOA records
  
   
• Additional CNAME records
  
   

Example

If the following record exists:

blog.example.com   CNAME   example.com

Then no other DNS records can exist for blog.example.com.

For example, the following configuration would be invalid:

blog.example.com   CNAME   example.com

blog.example.com   MX      mail.example.com

This restriction exists because a CNAME functions as an alias, meaning the hostname is entirely redirected to another domain.

Exception: CNAME Flattening

Some DNS providers support a feature called CNAME flattening. With this feature, the DNS provider resolves the CNAME target internally and returns the resulting A or AAAA records to the resolver.