You would only need a virtual domain in Apache if you're going to run some type of webmail application (SquirrelMail, Roundcube, etc.)
The hostname of
host.example.net is important for a couple of reasons. First, it allows you to assign specific services such as mail and web requests for your domain to be routed to particular servers if you need those services running on dedicated servers. Second, it allows that manipulation to be done in your DNS records rather than having to try routing specific ports to specific machines once the traffic reaches your network.
Just make sure that you put an MX record entry in your DNS records so that mail service is properly routed. The MX record can point to your actual
hostname or it can refer to a CNAME record that points to your
A FQDN is any domain name that resolves to an actual
hostname IP address.
To clarify an example of DNS records you would need, it would look something like:
example.net IN A 220.127.116.11
server01.example.net IN A 18.104.22.168
mail.example.net IN MX server01.example.net
www.example.net IN CNAME example.net
I'm ignoring the TTL and the MX priority values as you will set those when modifying your DNS and can use the default TTL value; an MX priority of
10 is pretty standard.