Regardless of how the world changes, email remains one of the most popular and effective marketing channels. A whopping 72% of consumers prefer to have brands communicate with them via email, and recent studies estimate that email marketers achieve as much as $38 in ROI for every $1 spent.

With numbers like these, it’s clear that email is just as relevant and valuable as it’s ever been. And yet there’s one very basic step that many marketers fail to master in their quest for email success: simply hitting the inbox in the first place.

If email doesn’t reach the inbox, brands lose the ability to connect with customers and ultimately make a sale—so every message counts. But recent Return Path research shows that 21% of email fails to reach its intended target. That’s one out of every five emails sent.

So what’s causing this massive fail, and what can marketers do to make sure their email gets delivered?

Understand what stands between you and the inbox

Today’s consumers have dozens of options when it comes to choosing an email platform, so mailbox providers do everything they can to provide an outstanding user experience. In particular, they carefully analyze every message and every sender that attempts to reach their users, to ensure that only legitimate and wanted mail lands in the inbox.

To help in this monumental task, mailbox providers have developed complex and ever evolving spam filtering algorithms. Every mailbox provider’s algorithm is unique, but certain factors weigh heavily in the calculation. One of those critical factors is sender reputation.

Know what factors into your reputation

Sender reputation is one way that mailbox providers can judge whether or not a sender is legitimate. While no two mailbox providers evaluate sender reputation the same way, they all incorporate similar elements.

  1. Complaints: Spam complaints provide a clear signal to mailbox providers that a sender’s messages is unwanted. As the rate of complaints generated by a sender increases, mailbox providers begin to filter incoming mail from that sender to the spam folder.
  2. Spam traps: Spam traps are email addresses that are used to catch spammers. Typically they were either once used by a person and then abandoned (recycled) or they are addresses that were never used by a person, created solely to catch spammers (pristine). Having spam traps on your list indicates to mailbox providers that your acquisition practices or list hygiene are not up to par.
  3. Unknown users: Unknown users are addresses that don’t exist or were recently abandoned by a user. When marketers mail to these addresses they receive a hard bounce code informing them to stop sending to that address. Continuing to send to those addresses is viewed as spammy behavior.
  4. Send volume: Mailbox providers monitor the volume of email sent by each sender. Consistency is key! Large spikes in volume are viewed with suspicion and can lead to throttling and filtering by mailbox providers.
  5. Blacklists: Blacklists are lists of IP addresses and domains that have been reported as known sources of spam. Mailbox providers run incoming IP addresses and domains across multiple blacklists to see if they have been listed. Your reputation will take a hit if you show up on a blacklist.

Recognize how reputation impacts deliverability

Sender reputation is a valuable tool for mailbox providers, but it’s also critical for marketers to understand their own reputation. Otherwise you could end up with poor inbox placement and not understand the reasons why. At Return Path, we’ve created a free reputation tool—Sender Score—which incorporates the same elements mailbox providers use in their own calculations. Sender Score evaluates a sender’s IP address and produces a score between zero and 100.

In a recent study, we looked at the impact of sender reputation on deliverability and found that inbox placement increases with improved sender reputation—especially at Gmail, Microsoft and Yahoo. Senders scoring above 91-100 (the best possible reputation score) had significantly more of their messages delivered to this inbox, while those scoring below 90 saw more mail diverted to the spam folder.

Take steps to improve and maintain your sender reputation

A poor sender reputation will keep your messages from reaching the inbox. It’s important to not only build up a strong reputation, but also maintain that reputation to achieve consistently high inbox placement. Take these steps to make sure mailbox providers consistently recognize you as a reputable, legitimate sender:

Sign up for feedback loops

Feedback loops are services that notify you when a subscriber complains about your email using the “this is junk/spam” button. Most mailbox providers offers their own feedback loop service. Sign up with the mailbox providers that are most frequently used by your subscribers and then take steps to limit the impact on your program by immediately removing or suppressing any subscribers who mark your email as spam.

Immediately remove unknown users

Identifying unknown users is fairly simple. When you send mail to an unknown user, you’ll receive a hard bounce code and an explanation of why the message was not delivered. These unknown users are abandoned or invalid addresses, meaning there is no subscriber at the other end and they provide no value to your email program. As soon as you receive a hard bounce code, remove or suppress that subscriber from your list.


Keep your subscriber list clean

Sending to spam traps and inactive addresses will hurt your reputation. The quickest way to ensure a clean list is to run it through a list hygiene service, which will identify all bad addresses so you can remove them from your list. You can also do this manually—simply identify any addresses that have not interacted with your mail in the last 90 days and suppress or remove them from your list.

Know when you’ve been blacklisted

There are numerous blacklists and each mailbox provider factors different ones into their reputation calculation. Use a blacklist lookup tool regularly to make sure your IP addresses are not listed. If you find that you have been blacklisted, find out their delisting process, which is normally available on their website.

Monitor your reputation

Sender reputation is not static. Nearly any activity can influence your reputation. It’s important to continually monitor your reputation for unexpected drops. The sooner you know there’s been a decline in your reputation, the more time you’ll have to find and fix the problem before it can significantly impact your deliverability and hurt your bottom line.


This article originally appeared in the July/August 2017 issue of Direct Marketing.

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Tim Sather

Tim Sather

Tom Sather is senior director of research at Return Path.

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