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[[Main Page|Home]] > [[CentOS]] > [[CentOS 6.x]] > [[Postfix server configuration]] > [[Blocking SPAM at MTA level in postfix]]

Refer https://www.howtoforge.com/block_spam_at_mta_level_postfix and use section 2 Postfix 2.x configuration 

Then test by sending emails from popular providers such as Gmail, Yahoo, etc.  If you see log lines such as:
<pre>
   Sep 22 09:26:22 mail postfix/smtpd[12999]: NOQUEUE: reject: RCPT from mail-lf0-f50.google.com[209.85.215.50]: 554 5.7.1 Service unavailable; Client host [209.85.215.50] blocked using dnsbl.sorbs.net; Currently Sending Spam See: http://www.sorbs.net/lookup.shtml?209.85.215.50; from=<jitendders@gmail.com> to=<jitender@rekallsoftware.com> proto=ESMTP helo=<mail-lf0-f50.google.com>
</pre>
then it might make sense to remove corresponding blacklist.  For example after above log lines dnsbl.sorbs.net can be removed to allow incoming emails from Gmail


==How to query DNSBL blacklists using dig to check for blacklisting==

To query a blacklist use commands similar to:
<pre>
   dig +short -t any 50.215.85.209.dnsbl.sorbs.net
   dig +short -t any 50.215.85.209.zen.spamhaus.org
</pre>
Typically outputs that start with 127.0.0. indicate that given IP is known for sending spams.

Refer https://www.spamhaus.org/faq/section/DNSBL%20Usage#366




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