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 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.
AVERAGE SENDER SCORE AND INBOX PLACEMENT RATE BY INDUSTRY
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 senderscore.org.