At 10:22 -0400 5/6/07, Steve Morris wrote:
I don't know what reverse DNS is, and when I asked the service tech about
your previous recommendation of having a reverse DNS, he didn't know what I
was talking about, either.
Standard DNS checks to see what IP address is associated with a
hostname, so, when you try to connect to mail.domain.dom, the DNS
server will see what IP address is associated with that hostname.
For example, let's say that the IP address for mail.domain.dom is
127.0.0.1.
With reverse DNS, it's the opposite. The DNS server checks to see
what hostname is associated with an IP address. In our example, it
would take 127.0.0.1 and try to figure out what hostname is
associated with it.
If reverse DNS is setup, then it will be able to determine that the
hostname is mail.domain.dom. If reverse DNS is not setup, it will
not be able to determine the hostname, or it may find that it is
something other than what was expected, such as mail.thirdparty.dom.
In the case of spam blocking, a reverse DNS will be done on the IP
address to verify that it is coming from the expected hostname. If
it is not, or if there is no reverse DNS entry, then the mail will be
flagged as spam, and blocked or filtered accordingly.
A reverse DNS entry is done through the PTR record (pointer record).
RFC 1912 (February 1996) advises that every Internet host should have
a name and that the PTR and A records must match.
Dan
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