The biggest tell-tale sign of a spammer is the huge quantity of their lists and huge lack of quality.  Since spammers have huge databases they don’t care much (if at all) about how many dead email addresses their databases have.  If they have 10 million emails in their database they don’t really care if 2 or 3 million of the emails no longer exist because they’re still emailing and reaching a colossal number of people (or at least hoping to do this). 

Even mass emailers who have divided their emails into smaller groups by industry or personal interest still have this problem.  I have an associate who recently bought an email database of US Mortgage Brokers from a well known mass mailer and 50% of the database were dead emails.  This can happen with supposedly reputable database vendors who specialize in B2B email databases.  One company online offers an email database of 1.4 million US real estate professionals, but only about 400,000 emails in the database actually still exist.

So the next question is: who determines your email reputation?  Email reputation is determined by a new breed of company called Reputation Service Providers (RSP).  These are companies who aggregate email recipient data from a large number of email providers for determining your email reputation.  Each of these email providers regularly gives data to RSPs on what their users have done with your emails.  In particular, they report to what extent users have opened and clicked your emails along with any spam complaints they’ve made.  An RSP then combines all the data from all the email providers who have received your emails and creates a reputation for you, usually in the form of a rating or score.  The method for determining your email score is similar to the credit reporting system used for getting a loan: you build up a credit score over time through the various creditors you’ve had loans with.

Email providers sign up with an RSP to get data on people sending email campaigns to them so they can determine whether to spam filter their emails or not.  Examples of RSPs include SenderScore, Goodmail, Karmasphere, and Lashback.

I want to talk about an RSP called Return Path who’s SenderScore certification is the most widely used and therefore the most important today.  Return Path  publicly provides reputation data on any mail server IP addresses you want to look up on their site.  It’s the same idea as doing a Who-Is search on a domain.