Can I block based on Reverse DNS name or domain?
Question asked by Douglas Foster - 7/31/2019 at 2:32 PM
I want to block using Reverse DNS ends-with matches, but it does not seem to be possible.   Asking here because we are running an older version and testing v17, so I don't know what I don't understand.   I tried to search this forum and did not see anything that speaks to the topic as either an open request or an existing feature discussion.  

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Douglas Foster Replied
To elaborate:   I have two spam filters in front of SM.  Together they are adequate, but both have idiosyncrasies that make me want something better.   Going through the capabilities of SM 17, I was impressed by what is included, and began thinking that an SM Gateway configuration might be better than either of them.   Unfortunately, Reverse DNS filtering is a deal killer for me.   If I get spam from "server7.malware4u;com", I want to block all of their servers, not just the one that sent that message, so i need a block rule like "ends with malware4u.com".   We also use Reverse DNS for country blocking, such as "ends with .ru".   We have very little need for international correspondence, so we block a long list of country codes.   Reverse DNS can be fraudulent, but it is usually accurate and useful, and it blocks a lot of our incoming mail.

I have been reviewing the market offerings, and have been shocked and baffled by the number of products that offer IP Filtering without Reverse DNS filtering, or Reverse DNS filtering without IP filtering.

A good spam filter also needs a good message review capability, so the admin can decide which allowed messages should be blocked, which blocked messages should be allowed, and which rules should be changed to achieve the desired result.   SmarterMail has no log review for the administrator, and I don't think a sufficient log review tool can be constructed even if all of the relevant log files are in detail mode and optimally parsed.   
Ben Conner Replied
Hi Douglas,

I was able to indirectly support custom spam filtering by using the SM custom anti-virus feature.  While not ideal, that met my needs.  I wrote a small Powerbasic routine that gets passed a file of the content of each incoming email by Smatermail.  I then read it and evaluate it for spam content.  If it is spam, I move it from the original location to a spam folder.  Smartermail then looks in that folder after about 10? seconds and if it is missing, end of story.  It doesn't get delivered.

That has worked out very well for me.

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