Poor email deliverability can be costly, causing a brand’s emails to end up in the spam folder or blocked entirely instead of reaching their subscribers. While deliverability can sometimes feel out of a business’s control, inbox placement is actually governed by seven factors, all of which are directly or indirectly under their control.

Let’s talk about each one in turn.

1. Infrastructure

The servers, setup and controls used by a company’s email service provider (ESP) affects how mailbox providers perceive their emails, so choose wisely. Email authentication is also part of good email infrastructure. The good news is most ESPs automatically authenticate the IP addresses and domains used by their customers to send their email. Authenticating your email with both SPF and DKIM standards, as well as setting up DMARC records, is important to ensuring good deliverability, so it’s worth double-checking with your ESP to make sure that all three of those authentication elements are in place. 

2. Email Volume

The more email a brand sends, the more that mailbox providers scrutinize their messages. So, very large senders will naturally struggle more to maintain good deliverability than small senders will.

Sending patterns are also important, as it’s common for spammers to try to send a huge amount of email out of the blue. Inbox providers like to see predictable patterns in sending volumes from a brand over time. That doesn’t mean that brands have to send the same amount of volume each day or even each week, but relatively even patterns are good. This also means that brands need to slowly ramp up volume over weeks heading into higher email frequency seasons, such as the holiday season for retailers.

Here small senders also have an advantage, as they tend to send their emails over shared IP addresses along with several other small senders. This helps even out email volume, making it look more consistent to mailbox providers.

Related Article: How Many Marketing Emails Is Too Many Marketing Emails?

3. Content

While word choices, punctuation, and the balance of images and text in your emails used to be major email filtering factors, they are largely inconsequential now. Today, email code is the content that inbox providers pay attention to.

First, they don’t want to see any potentially malicious code, such as <embed> tags or JavaScript. Second, they want to see emails that are properly and cleanly coded, with all tags closed, for example.

And third, they heavily scrutinize URLs. If a brand’s emails include links to websites with poor reputations, their deliverability will suffer. If they use URL shorteners, which spammers often use to mask where they are linking to, they’ll similarly have problems.

4. Bounces and Spam Traps

Mailbox providers also want to see that brands are following good subscriber acquisition practices and not sending to bad addresses, of which there are two categories. First, they don’t want brands sending emails to too many email addresses that don’t exist. When senders do this, those emails “hard bounce” and their ESP automatically suppresses those addresses from receiving future campaigns. If more than 2% of a brand’s emails hard bounce during a month, that starts to hurt their deliverability.

And second, sending emails to even a few spam traps similarly demonstrates that a brand has poor subscriber acquisition practices, as these email addresses are used by inbox providers and blocklist operators to identify spammers. For example, pristine spam traps are email addresses that are hidden on the internet in places where only email scraping software will find them. So, sending to these addresses demonstrates that a brand is either using such software or buying lists from people who do. Either way, that’s a big red flag for mailbox providers.

5. Spam Complaints

So far, we haven’t talked at all about the reaction of email users, which is, of course, critical. Negative reactions in the form of spam complaints are the oldest form of subscriber feedback. Brands want to keep their spam complaint rates low. Very low.

If more than 0.1% of a brand’s subscribers report their emails as spam, they may experience blocking or junking. Unfortunately, subscribers report senders’ emails as spam for a wide variety of reasons, including not opting in, not being able to easily unsubscribe or not trusting a brand’s unsubscribe process, or simply no longer wanting those emails. Even so, most reputable brands are able to easily stay well under that threshold.

Learning Opportunities

Related Article: What's Going to Solve the $20B SPAM Problem?

6. Engagement

Today, it’s not just negative feedback that mailbox providers pay attention to. They also heavily weigh positive feedback in the form of opens and other behaviors that indicate their users want to receive a sender’s emails.

In fact, positive engagement has become one of the most important factors affecting deliverability. Because of that, it’s imperative for senders to manage their inactive subscribers, reducing email frequency to less active subscribers and eventually suppressing subscribers who haven’t engaged in a long time. Sending more segmented, personalized, and automated campaigns can also boost engagement rates and help deliverability.

Unfortunately, Apple’s Mail Privacy Protection will seriously complicate senders’ ability to see opens, which has been central to engagement management since mailbox providers started factoring in engagement. By creating false opens for every email sent to Apple Mail users who enable Mail Privacy Protection, Apple makes it very difficult to accurately identify inactive subscribers.

7. Reputation

The final factor is sender reputation, which each mailbox provider calculates according to their own unique and secret weighting of the earlier six factors and their sub-factors. This reputation is not only attached to the IP addresses used by a sender, but also to the domains that they use.

Evolving Spam-Filtering Algorithms

As email behaviors and spammers’ tactics change, mailbox providers fine-tune their filtering algorithms, tweaking the role of each of these factors and their sub-factors. There have been many changes over the years, but two have fundamentally altered how marketers manage their deliverability.

First, the introduction of engagement-based filtering made it so brands can no longer thrive by simply not angering recipients. This ended the practice of senders bloating their lists with inactive subscribers who didn’t engage but also didn’t complain. Today, marketers must always balance quality with quantity when it comes to their email audiences.

And second, the introduction of domain-based reputations made it so brands can no longer run away from poor sender reputations by simply migrating to new IP addresses. Today, senders who get into deliverability trouble have to change their behaviors to get back in mailbox providers’ good graces.

Because of those two changes, it’s wise for marketers to keep a watchful eye on all of these factors that impact deliverability to avoid trouble in the first place.

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