You get a crazy email like this:

IMPORTANT: Do not ignore this email.
 
Your hostname (server.domain.com) could not be resolved to an IP
address. This means that /etc/hosts is not set up correctly, and/or
there is no dns entry for server.domain.com. Please be sure that
the contents of /etc/hosts are configured correctly, and also that
there is a correct 'A' entry for the domain in the zone file.
 
Some or all of these problems can be caused by /etc/resolv.conf
being setup incorrectly. Please check that file if you believe
everything else is correct.
 
You may be able to automatically correct this problem by using the
'Add an A entry for your hostname' option under 'Dns Functions' in
your Web Host Manager.

The above simply means that no DNS record can be pulled for the hostname 'server.domain.com', this can be corrected this way:

1. Login to WHM as root
2. Navigate to Edit DNS Zone and select the domain the e-mail contained
3. Create an A record that says "server" with the first IP address of the server (listed first in welcome e-mail for the product)

Done! Please note that the "server" hostname can vary depending on what hostname do you have set, this guide assumes that it is "server.domain.com", while it may be different for you, following this guide will still help you correct the issue.

See also Logging Into WHM, Set Up Custom Nameservers