Here’s How Sender Reputation Impacted Email Performance in 2018

August 28, 2019

This article is included in these additional categories:

Customer-Centric | Digital | Email | Featured | Privacy & Security

Every year spammers find it more difficult to get their emails into inboxes, thanks to efforts made by email providers. Last year only 16% of emails came from the least reputable senders – a figure down from 25% in 2017, per Return Path’s latest benchmark report [download page] on the state of email reputation.

In 2018, more than one-third (36%) of the messages analyzed were sent by the most reputable senders, as defined by those with a Sender Score above 90. Sender Score is Return Path’s free reputation calculation service, and it carries a 0-100 rating. To arrive at its conclusions, Return Path analyzed more than 4 trillion emails sent last year from IP addresses whose Sender Score was calculated, and whose subscriber engagement and inbox placement data were available for analysis.

Which Metrics Affect Sender Reputation?

There are three main metrics that affect sender reputation, according to Return Path: complaint rate; unknown user rate; and spam trap count.

Complaint Rate

Senders with a reputation score of 91 and higher averaged a complaint rate (where the recipient marks the email as junk or spam) of just 0.9%. That was markedly below the range for other Sender Scores, with the least reputable senders (a score of just 1-10) averaging a dismal 6.3% complaint rate.

It is worth noting that, according to the report, the average complaint rates for senders scoring between 11 and 100 more than doubled from 2017.

Unknown User Rate

Email list quality also impacts reputations, per the report. Unknown users are email addresses that never existed, have been terminated by the mailbox provider or abandoned by the mailbox user. Senders that maintain a high rate of unknown users in their database are perceived to have poor list hygiene, which affects their reputation.

Senders with the best reputation (91-100) kept clean lists in 2018, averaging an unknown user rate of 0.9%. Senders with scores of 50 or below, however, had an unknown user rate that ranged between 5-8 times higher. Senders with a score of 21-30 recorded the highest unknown user rate, of 8.2%.

Spam Traps

Spam traps, according to Return Path, are decoy emails that don’t belong to active users or were once held by users but have since been abandoned and are used to find spammers and senders with poor data quality practices.

Although the gap between best and worst scores still exist, it’s not nearly as wide as last year. Senders with a score of 91-100 averaged just 0.41 spam trap hits, compared to 3.09 spam trap hits by senders with a score of 1-10 (down considerably from 7.52 trap hits in 2017).

Mailbox Providers Turn Away Messages from Low-Reputation Senders

Sender Score appears to be strongly correlated with the Average Delivered Rate, meaning that mailbox providers’ gateway filters are often bouncing or rejecting messages sent by mailers with lower reputation scores.

The results indicate that senders with a score above 90 (91-100) had an average delivered rate last year of 91%, meaning that 91% of their messages were not bounced or rejected by mailbox providers’ gateway filters. (This particular analysis does not identify what percentage of emails reached the inbox.)

The Average Delivered Rate dropped to:

  • 71% for senders with a score of 81-90;
  • 44% for those with a score of 71-80;
  • 28% for those with a score of 61-70; and
  • 15% for those with a score of 51-60.

Senders with a score of 1-10 averaged a delivered rate of just 1%.

Which Mailbox Providers Are the Most Lenient?

Microsoft was once again the most difficult mailbox provider to reach last year. Just 72% of emails sent by senders with the highest sender score (91-100) made it into Microsoft inboxes in 2018.

Some 88% of emails sent by those with the highest sender band reached Gmail inboxes. However, senders with lower sender scores were more successful reaching Gmail inboxes than previously. Some 26% of senders with the lowest sender band (1-10) successfully made their way into Gmail inboxes in 2018 compared to a low 8% in 2017.

By comparison, AOL, which remains the easiest provider to reach, has seen improvement. Per the report, AOL was acquired by Verizon Media Group and has migrated its email filtering to Yahoo, which has resulted in AOL inbox placement rates in some cases falling more than 50 percentage points.

The full report can be downloaded here.

About the Data: Return Path describes its methodology as follows:

“To conduct this study, Return Path analyzed more than 4 trillion messages sent during 2018 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”

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