[NBLUG/talk] Hosts file and spam filtering

Robert P. Thille list-nblug-talk at rangat.org
Wed Apr 22 10:31:31 PDT 2015

> On Apr 22, 2015, at 10:12 AM, Omar Eljumaily <omar at omnicode.com> wrote:
> 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
“host” uses DNS, not the system resolver.
To test what a “normal” host lookup does, try ‘getent’ as in:
    rthille at hostname:~$ getent hosts test.mydomain.com
    rthille at hostname:~$ getent hosts www.google.com
    2607:f8b0:4002:c03::6a www.google.com
    rthille at hostname:~$ 

getent is a Debian thing, I forget what package you need to install to get it, and other distros might not have it.

OTOH, I think putting a whitelist in Postfix might be a better approach, but I run qmail, so I can’t help you with that :-)


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