Reverse address entries

Barry Margolin barmar at
Tue Jul 2 15:32:19 UTC 2013

In article <mailman.737.1372773227.20661.bind-users at>,
 Daniel McDonald <dan.mcdonald at> wrote:

> The other place reverse DNS is routinely queried is SMTP.  If you care
> enough to send mail, you should care enough to set up your reverse entries
> realistically so that spam filters will recognize that you are trying to
> actively manage your email server and this isn't mail from a BOT...

Reverse DNS is generally necessary, but may not be sufficient. Your IP 
also has to NOT be on one of the many block lists. These lists are 
populated with IPs that have spamming history, as well as IPs that ISPs 
have volunteered as being used for residential services rather than 
commercial users.

I suppose it's obvious, but the other general place where reverse DNS is 
important is if you make use of hostnames or domain suffixes in filter 
files like hosts.allow and hosts.deny. If your hosts.allow file contains 
something like:

sshd: *

then the server will do a reverse lookup and forward validity check 
before testing whether the hostname ends in

Barry Margolin
Arlington, MA

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