How Sender Score Correlates to Delivered Rates

John Young, PhD
Director of Product Analytics

Return Path’s Sender Score reputation rank (available at is a measure of the reputation of mail coming from an IP address based on feedback from many ISPs and filtering companies that provide reputation data to Return Path (over 150 million mailboxes). As regular readers of this blog know, the major driver of inbox placement is reputation. But saying that is one thing – actually understanding your sending reputation is another. We created the Sender Score to give senders a number that would help them quantify their reputation to make it easier to understand and therefore easier to manage.

Does it work? We decided to do a little test to find out.

Our findings: Yes, it does work. There is a strong (positive) linear relationship between a mailer’s reputation score and their corresponding delivered rates at the ISPs that participate in our reputation network. You can see the results in the chart below. As delivered rates increase the average reputation score increases, and vice versa.


This means that your IP’s reputation score can be a useful measurement when determining how well you’re doing, but it is by no means the final word on the fate of your email. Remember, these are statistical models based on looking at millions of IP addresses. Individual results can and do vary.

Does this data that mean that a low Sender Score reputation rank causes low delivered rates? Simply put, no. The majority of the ISPs in the network are just testing (not using) the summary score as part of their decision making. We are proud to say that an increasing number are starting to use the score. However, the correlation doesn’t surprise us. Our “summary score” is constructed from many of the same elements that ISPs use to determine whether or not to block or throttle messages coming from a particular mail server. Meaning that they aren’t blocking messages because of a low score. They are blocking the messages for the same reasons that result in that IP having a low score.

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