Email engagement metrics: reputation ‘key to mailbox provider checks’

A mailbox provider’s primary goal is to deliver the messages their users want while keeping unwanted and potentially damaging content from their inboxes. To decide which emails to deliver, many mailbox providers (MBPs) will take a multi-layered approach.

Firstly, they will check a sender’s email reputation to judge whether mail being sent is legitimate and wanted by their users. Sender reputation is calculated using a variety of metrics, with each MBP using their own formula to judge whether or not to accept incoming mail and where it should be filtered to. They will then typically perform authentication checks, making sure the mail meets any published Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM) or Domain Message Authentication Reporting and Conformance (DMARC) records, which provide greater assurance of the sender’s identity.

Finally, they will take a more detailed look at what content is being sent and how the subscriber engages with it. It’s therefore worth noting that if a sender fails at the first check, it’s likely their email will not be accepted by the mailbox provider.

Identifying sender scores

One way marketers can find out how reputable they are as a sender is by using Sender Score. Like a credit score, it is an evaluation of a marketer’s sending practices compared to other senders. Determining message and email programme quality with a rating from 0 to 100, Sender Score uses data points and reputation formulas similar to those MBPs use, to give an accurate representation of how they view emails. It works in the same way that a person with well-managed finances will have a high credit rating. If a marketer looks after its email reputation by ensuring they have healthy metrics – ie. low complaint rates, high subscriber engagement and minimal industry blacklists – then their sender score will be high.

In 2016, senders scoring above 90 managed to get, on average, 92 per cent of their messages past MBP gateway filters. 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 [see graph, right]. While not ideal for senders, it shows that MBPs’ filters are working as intended. Senders with a poor reputation and questionable sending practices are being successfully blocked from users’ inboxes.

Email engagement metrics – sender reputation

While each MBP determines sender reputation using their own formula, there are some metrics that all weigh heavily into their calculations. Among these are complaints, spam traps, unknown users and engagement.

Complaints can originate from various sources for a variety of reasons. Most MBPs will have a ‘this is junk/spam’ button that recipients can easily click on. These votes indicate to MBPs that the content being sent is undesired, which will subsequently affect deliverability rates. In 2016, brands with a Sender Score above 90 had an average complaint rate of less than one per cent [see graph above left]. Most MPBs recommend no higher than a 0.2 per cent complaint rate. Best-in-class senders should be aiming for <0.1 per cent.

Unknown users can also negatively impact email deliverability. An unknown user is an email address that never existed, has been terminated by the MBP, or was abandoned by the user. If an email is sent to an unknown user, MBPs will return a hard bounce code (5xx). Senders that not only retain unknown users but send to a high percentage of them are perceived by MBPs as having poor list hygiene practices, which will lower their sender reputation. In 2016, senders scoring 80 or below had unknown user rates ranging from eight to 11 per cent. Senders scoring above 90 have retained a relatively low average unknown user rate of one per cent [see graph below right].

In addition, spam traps can be a problem for marketers. These 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, while recycled spam traps are addresses that were once held by a user, but have been reclaimed by MBPs to do the same job. While spam traps were more commonly found on the lists of lower scoring senders, a few higher scoring senders have kept the average above zero by retaining a small number on their lists [see graph below left].

Finally, subscriber engagement is taken into account – albeit differently, depending on the MBP. For years, the likes of Gmail, Microsoft, Yahoo, and AOL have been considering the way subscribers interact with their emails and using this to help determine deliverability. Currently, Gmail is the most heavily influenced by engagement levels, followed by Microsoft, then Yahoo and AOL. Read rates, open rates and deleting without reading rates are examples of metrics that are becoming increasingly important to MBPs who want to ensure that every email delivered is desired by the subscriber.

As such, it’s no surprise that Gmail and Microsoft inboxes are the hardest to reach. Only brands with a Sender Score above 90 can exceed the global inbox placement average (79 per cent), while the rest fall below 70 per cent inbox placement [see graph right]. Yahoo inboxes are slightly more accepting, with inbox placement above the global average for senders scoring over 80. AOL, on the other hand, will accept senders scoring as low as 30, which means a lot of its subscribers will be receiving emails they would mark as spam.

Sender reputation by industry

When comparing different industries, there are some that stand out more than others when it comes to email reputation. By analysing sender scores and Inbox Placement Rates (IPRs) of more than 17,000 commercial senders, the utilities industry comes out on top, with a Sender Score of 97 and an IPR of 93 per cent [see graph below]. This is followed by the travel, recruitment, insurance and clothing industries. There could be a number of reasons for this. For example, these industries’ end objectives tend to involve a high value transaction – either a holiday or commission on a job – which means they could take greater care at ensuring their emails are reaching the intended recipient.

As email marketing continues to evolve, MBPs have enhanced their acceptance criteria, relying on engagement-based metrics to identify which senders should be sent to the inbox, and which should be filtered to the spam folder. It’s important that marketers do not underestimate the impact of subscriber complaints, unknown users and spam traps. Email reputation is a delicate ecosystem which requires constant management and fine-tuning. Indeed, marketers increasingly require full insight into their email journey and how their emails are being perceived in order to ensure their emails are reaching their subscribers’ inboxes.

Have an opinion on this article? Please join in the discussion: the GMA is a community of data driven marketers and YOUR opinion counts.

Read also:

It’s big, but it’s not clever – email overkill: retailers should stop the spam

Using personalisation and contextual marketing to transform email marketing campaigns