[NBLUG/talk] Hosts file and spam filtering

Omar Eljumaily omar at omnicode.com
Wed Apr 22 10:12:11 PDT 2015

Anybody an expert on DNS and Postfix spam filtering?  My problem is that 
I use smtpd_client_restrictions check_reverse_client_hostname to check 
for senders that don't have a reverse client host name.  It blocks an 
average of about 3,000 potential spam requests per day, so I consider it 
very effective.

The problem is that there are a few admins who refuse to configure their 
mail servers properly, so I'm left trying to create a white list for 
these few senders.

The easiest way I thought of doing the white list is to use the 
/etc/hosts file to kluge in a reverse lookup.  I've seen docs that talk 
about reverse lookups in hosts files.  However, I'm having a more basic 
problem.  I try to enter something like:    test.mydomain.com

Then use the command:

host test.mydomain.com

The result comes back as a non-existent domain.

This is Centos 6.6.  I'm in the process of switching to Ubuntu, but that 
hasn't happened yet.

Am I missing something with the /etc/hosts file and using the host command?

I know that I can use a DNS server as well.  I'd like to try to avoid 
that because I only want the mail server to use that reverse lookup.  
Also there are other Postfix solutions, but they all seem complex.  
Worst case is that I have a custom Milter that can do the reverse 
lookups itself.  I'd rather use the stock Postfix solution, though.



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