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Stop Spam with Grey Listing in SmarterMail

Posted on Apr 17, 2008 by Paul White

When I first heard the phrase grey listing. I thought that was when you send someone an email, and the server emails you back saying please click on this link and fill out this form.  You had to validate yourself before your emails would reach your friend or client.  Even though this will stop most all spam. it will also stop all the email campaigns that you might want to get.  Plus it would also result in an email being sent out, for everyone being sent in.  I thought this was horrible and so I never implimented it on smartermail

But later after reading about how other Server Admins have had success with Grey Listing. I thought maybe there is more to it.  So I read up on it and learned that its very different from what I had perceived. 

An analogy on Grey Listing
Lets say your mail Server is a Bar. People come up to the front door of your bar and go right in and have a drink.  But after a while your bar starts to get popular, and someone sneaks a gun into your bar.  So you get a bouncer to check everyone for guns before coming in.  This would be the equivalent of an RBL Lookup.  This has been one of the many ways to check the history of the IP that is trying to send you mail.  But now lets say your bar is getting really popular.  So you start to run it vegas style.  Meaning if you aren't on the list ( whitelist ) you get to wait in line for an hour or more before getting in.  This is what grey listing does.  It makes everyone wait in line before getting in. 

Why does grey listing work?
Its simple time is money.  If you spend an hour waiting in line, you are spending an hour doing nothing. You could have been somewhere else making money, or having a good time.  The same applies to Mail Servers.  When legit mail Servers do a Blast out.  The emails initially go into their Queue.  Next they try to send this email to the receiving server.  If the server comes back with a busy message, they keep the message in the queue and try again later.  Spammers on the other hand are not justing sending a few thousands emails.  They are sending millions.  They can't afford to have emails sitting in a queue waiting to go out.  Why? Because millions of emails sitting in the queue could crash their server.  They would rather just delete the emails that have any issues, than to try again later.  So as a result by telling the Spamers that you need to wait in line, they will just give up and leave. 

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