Director's Blog


Emails and RBLs

A good or a bad thing?

I recently increased security for our mail servers by adding checks to RBLs.

Realtime Blackhole Lists, or Reputation Block Lists contain thousands of blacklisted IP addresses, addresses that may have been used by spammers and hackers.  When an email arrives at the mail server a request is sent to an RBL to see if the sender’s IP address is listed on it.  The email will be rejected and “bounced” back to the sender if a match is found.

Since 95% of all email is generally spam, it is important to try and stop as much as possible from arriving in the user’s mailbox. 

More and more mail-server administrators are adopting the use of RBLs so it is important for ISPs to keep their IP addresses clean. 

I have had some of my servers blacklisted in the past and had to ensure there were no vulnerabilities or exploits active on my server before they would de-list me. I do not wish to repeat that experience.

Recently, some of my clients complained that they had not received an email they were expecting.  On further investigation, it turns out that the sender is on a blacklisted IP address.

I believe the responsibility lies with the sender to ensure they are not blacklisted.  Having had the reverse happen to me, my clients looked to me to correct the problem of them being blacklisted, and quite rightly so in my opinion.

I now have a dilemma since some clients appear reticent to tell their contacts that they are the cause of the problem and are asking me to relax my security.  

$1·If I remove the RBL checks we will have an increased amount of spam being processed by the server.  We used to have a lot of complaints about the amount of spam getting through to mailboxes before we started using the RBL checks.

$1·Without the RBL checks we stand a greater chance of our server getting blacklisted due to spam being allowed to run free as such. There is an increased possibility of backscatter too.

$1·If our server gets blacklisted and our clients send an email out to another mail server that uses the RBL checks, the emails will bounce back undelivered.

$1·Rejecting blacklisted mail before it is processed by spamassassin means our server will run more efficiently.  A more efficient server means websites are server/load faster, which means they will rank better on Search engines such as Google who place speed highly in their ranking algorithm.

As you can see, I am between a rock and a hard place on this one.

I have since employed a few alternative/additional methods to combat spam on our servers that will hopefully be less aggressive.  

That said, any contacts that receive a bounce with a blacklist notification must contact their own service provider to resolve the problem.  The onus is entirely on them to do this, as it has nothing to do with the services we provide.