2017 Sender Score Benchmark Report

See Return Path’s latest annual report analyzing the most influential factor that determines if and where email is delivered: sender reputation. If you don’t know your Sender Score, look it up here and then come back and follow along.


A mailbox provider’s main goal is to deliver the messages their users want while keeping unwanted and potentially damaging content from their users’ inboxes. To do this, mailbox providers use a sender’s reputation to judge whether mail from that sender is legitimate and wanted by their users. A sender’s reputation is calculated using a variety of metrics, and each mailbox provider has their own formula to judge whether or not to accept incoming mail and where to filter it.

Marketers who are aiming for the inbox use Return Path’s Sender Score to discover and track their sender reputation and learn how mailbox providers perceive their messages. Similar to a credit score, Sender Score is an evaluation of your sending practices compared to other senders to determine the quality of your messages and your email program. A marketers sender score is rated from 0 to 100. Sender Score uses data points and reputation formulas similar to what mailbox providers use to give a relatively accurate representation of how mailbox providers view your email.

In this report, we will show the impact of reputation and Sender Score on email performance, including:

  • The average delivered rate
  • The impact of complaints, spam traps, and unknown users
  • The average inbox placement rate at Microsoft, AOL, Gmail, and Yahoo
  • The average Sender Score and inbox placement rate by industry


A sender’s delivered rate measures the percent of messages that weren’t bounced or rejected by mailbox providers’ gateway filters. The delivered rate does not show which folder the messages were then delivered to—primarily the inbox or the spam folder—but it does factor out any messages that have no hope of being seen by subscribers.

In 2016, senders scoring above 90 managed to get, on average, 92 percent of their messages past the gateway filter. Meanwhile, senders with scores of 80 or below saw more than half of their messages rejected by the gateway filter—and presumably less actually reached customers inboxes. While not ideal for senders, it also shows that mailbox providers’ filters are working as intended. Senders with a poor reputation and questionable sending practices are being successfully blocked from users’ inboxes.



While sender reputation is based on many different metrics—with each mailbox provider using their own formula—there are some metrics that all mailbox providers weigh heavily into their calculations. Among these key metrics are complaints, spam traps, and unknown users.


A complaint is generated when a mailbox user marks a message as junk or spam. A high complaint rate signals to mailbox providers that the sender’s content is unwelcome and should be sent to spam.

In 2016, senders scoring above 90 had an average complaint rate of less than one percent. Most mailbox providers recommend no higher than a 0.2 percent complaint rate.


Complaints can originate from various sources for a variety of reasons. Read the Marketer’s Guide to Subscriber Complaints to understand where complaints are coming from and why.

Unknown Users

An unknown user is an email address that never existed, has been terminated by the mailbox provider, or was abandoned by the mailbox user. Mailbox providers will return a hard bounce code (5xx) indicating when email is sent to an unknown user. Senders who not only retain unknown users but send to a high percentage of them are perceived by mailbox providers as having poor list hygiene practices, which will impact their sender reputation.

In 2016, senders scoring 80 or below had unknown user rates ranging from eight to 11 percent. Senders scoring above 90 have retained a relatively low average unknown user rate of one percent.


Spam Traps

Spam traps are email addresses that don’t belong to active users and are used to identify both spammers and senders with poor data quality practices. There are two types of spam traps: pristine and recycled. Pristine spam traps are created solely to capture bad mailers. These email addresses were never owned by a real person and therefore shouldn’t be on any marketer’s list. Recycled traps are addresses that were once held by a user, but have been abandoned and converted into spam traps.

While spam traps were more commonly found on the lists of lower scoring senders, a few higher scoring senders kept the average above zero by retaining a few spam traps on their list.

The chart above shows that IP level reputation filtering is still important in spam filtering algorithms at mailbox providers, as IP addresses with a higher Sender Score generally receive better inbox placement, particularly at Gmail, Yahoo, and Microsoft. Marketers who ignore complaints and retain spam traps and unknown users on their list will come to find their email banned from the inbox as those metrics begin to impact their sender reputation. But at these four mailbox providers, a high Sender Score on its own doesn’t translate to higher inbox placement rates. This is due to engagement filtering, a mailbox providers own reputation calculations, as well as the content in the incoming message, which aren’t included in Sender Score calculations.



In addition to the overall state of email reputation, we also wanted to take a closer look at the average performance by industry. The chart below shows the average Sender Score and inbox placement rate of over 17,000 commercial senders, broken out by industry. As only legitimate commercial senders are included, these numbers are a better reflection of how each industry is performing. They also provide a more accurate benchmark for marketers to evaluate their program.



To conduct this report Return Path analyzed over 4 trillion messages sent during 2016 from IP addresses whose Sender Score was calculated, and whose subscriber engagement and inbox placement data were available for analysis. In addition to Sender Score data, this report used data from the Return Path Reputation Network to track inbox placement rates across mailbox providers, and the Return Path Consumer Network to identify the Sender Score and inbox placement rates of more than 17,000 commercial senders. Data used for this report is aggregated and anonymized, and is not limited to Return Path clients. Sender Score is a free reputation calculation service and is available at