A reverse DNS record (also know as a PTR record), is a reverse
mapping from IP to name. For instance, when a lookup is made on the IP
of 1.2.3.4, it should come back with host.mydomain.com. It is a very
good idea to have the hostname of your server match the PTR record
assigned to it’s IP. This can only be changed by the owner of the IP
address (The Planet, in the case of IP’s assigned by us).