If you’ve noticed your deliverability declining in recent years, you’re not alone.

In 2014, one in six commercial emails failed to reach the inbox. In 2016, that number jumped to one out of every five. That’s right – worldwide, just 79% of commercial email reaches its intended recipient. The numbers are even worse for US brands, where just 73% of commercial emails reached the inbox in 2016. The rest are filtered to spam, or simply go missing.

After 45 years, email may not be as flashy as other channels, but it remains the foundation of most digital marketing programs, and consumers prefer hearing from brands via email. Hitting the inbox is more critical than ever, so it’s important to understand what’s causing deliverability to slip.

Engagement-based filtering

Ultimately, mailbox providers want to ensure a positive inbox experience for their users. This means delivering emails that are legitimate and wanted to the inbox while sending unwanted messages to the spam folder. To help with this task, mailbox providers like Microsoft, Google, Yahoo, and AOL are placing increased focus on subscriber engagement metrics for their filtering decisions.

Engagement metrics look at how users interact with messages from a given sender; things like how many messages are read, replied to, forwarded and deleted without reading. By understanding how subscribers engage with a sender’s email, mailbox providers are better able to determine which emails are wanted by subscribers and which should be diverted to the spam folder.

Changing expectations

As email volume continues to rise, consumers face a constant struggle with inbox overload. Most people spend just a fraction of a second deciding whether to open, ignore, or delete a given email. And if they do choose to open your email, they expect timely, relevant content. Mass produced emails that don’t reflect the subscriber’s preferences will be quickly deleted and may even produce spam complaints.

The lesson here is that subscribers have high expectations. If you don’t meet those demands, your email won’t be opened. Over time, those ignored and deleted emails will add up to a disengaged subscriber and possible spam filtering.

Clearly, having a loyal, engaged subscriber base is more important than ever before. But that’s really nothing new—creating relationships has always been the key to business success.

Here are four things you can do to maximise subscriber engagement and ultimately improve deliverability:

Set appropriate expectations

As part of your opt-in process, give subscribers the opportunity to tell you what kind of content they want to receive from you, and how frequently. Make sure they understand what they can expect from your email program and then follow through on those promises.

The “get to know you” period is a critical time in the subscriber relationship. If your email communications don’t match the subscriber’s expectations you’ve set, it will be difficult to regain their trust.

Create a consistent brand experience

There’s a reason stores and restaurants strive to create a consistent experience with every visit—and the same is true with email. Every message should have a consistent look and feel that’s clearly associated with your brand, to establish trust and create a sense of familiarity. If subscribers have doubts about where a message is coming from and whether it’s legitimate, they’re far less likely to engage.

Keep your sending list clean

The idea is simple: to maximise engagement, you should only send to people who actually want to hear from you. Build your list through legitimate means, and promptly remove any email addresses that produce a hard bounce or complaint. Sending to unknown users or spam traps is a sure way to get your email sent to spam or blocked. You can quickly and easily check your entire existing list, as well as verify new addresses in real time, using a list validation service.

Take immediate action on spam complaints

You wouldn’t keep talking after someone clearly asks you to stop, and you shouldn’t continue emailing a subscriber who has reported your email as spam. Spam complaints are one of the most significant factors in deliverability, as they provide a clear indication that your mail is unwanted. If your complaint rate exceeds about 0.1%, increased spam filtering and blocking are likely to follow.

To minimise the impact of complaints, make sure you’re subscribed to all available feedback loops and immediately remove subscribers from your list if they complain.

The bottom line is, if you want to reach the inbox, you need an engaged subscribers. And in order to keep subscribers engaged, you need to treat them like real people. Get to know them, figure out what they’re interested in, and listen when they give you feedback — whether that’s in the form of an opened email, a purchase, or a spam complaint.