FQDN for server with various domians

Question

I have a question regarding setting the FQDN on a server, well, technically, a vserver that serves a variety of domains.

I have understood that the FQDN is a globally unique address that points to a specific computer/host in the internet. So, if I had a subdomain test for the domain domain.com then I could set my FQDN to test.domain.com if that server would serve solely to that subdomain.

Currently my FQDN is localhost.localdomain which seems like something that is a very bad idea. I am having issues with email responsiveness, I would not be surprised if my current FQDN has something to do with this.

My question is: What is the appropriate way to set a FQDN for a server that serves a variety of domains? I would think that the server should be given a FQDN by the company who runs the server. Can just pick any FQDN, no matter what?

I hope that you can shed some light on this matter...

Answer 1

FQDN is a globally unique address that points to a specific computer/host

This is actually wrong. As an example, with Round Robin DNS, a FQDN can point to multiple computers. The "fully qualified" in FQDN just means that it's not just a host name like mail or www, but includes the full domain, e.g. mail.example.com.

I am having issues with email responsiveness, I would not be surprised if my current FQDN has something to do with this.

No. What you use as FQDN for your host is actually not all that important. Much more important is how you configure DNS records (e.g. MX) and your MTA. These must be aligned with each other, but how to do this is much too broad for this format.

What is the appropriate way to set a FQDN for a server that serves a variety of domains?

It should be name that is resolvable via DNS and pointing to your host (and is not a RR-DNS record), but other than that, it doesn't matter. Even if you keep it as localhost.localdomain and your MTA and DNS are set correctly, this will not affect many things (like SMTP and HTTP traffic).