Let us say we own the zone mywebservice.com.
I would like each of my customers to get their own subdomain, such as customer.mywebservice.com.
customer.mywebservice.com needs to be a CNAME to a given server offsite. Since that site manages its own equipment and can change addresses at any point in time, the CNAME is a requirement.
People also need to be able to send email to inbox@customer.mywebservice.com, which would require a simple MX record.
However, and this is where I'd like some guidance:
According to RFC 1034:
If a CNAME RR is present at a node, no other data should be
present; this ensures that the data for a canonical name and its aliases
cannot be different.
I have also verified that my DNS server will refuse to serve up anything but a CNAME for hosts that use them.
So, it seems that I may have a losing situation. If I want to use the MX record, I need to use an A instead of a CNAME.
Can anyone think of any workarounds? Thanks!
Best Answer
Unfortunately, what you're running into is a limitation of the DNS specification. Having an MX record for the same hostname as is defined as a CNAME record will fail in most DNS server implementations. Some older DNS servers will allow this, but they have been mostly phased out in favor of newer, more secure implementations.
Instead of using CNAME records, you will need to use 'A' records with the IP addresses of the customer sites directly instead of aliasing the names.