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It’s one of the great mysteries of email marketing: Why do some emails go to the inbox while others land in the spam folder? Although each sender’s situation is unique, some general issues affect where your email goes.

Fortunately, you can correct just about every factor that affects your deliverability – your ability to reach the inbox. But first, here’s a primer on what goes into deliverability and what’s keeping your messages out of some inboxes.

  1. How receivers work

A receiver is a corporate email server or webmail provider such as Gmail, Yahoo or Hotmail. Each of these uses a set of rules – its own or an outside filtering system – to filter out spam.

Your individual recipients are like receivers, too, because ISPs like Gmail, Yahoo and AOL factor their actions on your emails into their filtering decisions. You have to appease both in order to hit the inbox consistently.

  1. How ISPs detect spam

Network-level email receivers check several factors when detecting spam. Some are elements in the message itself, but more often now ISPs use your sender reputation. They do this to decide firstly, whether to accept your email and then if it should be routed to the inbox or the bulk folder.

If a receiver or anti-spam service blocks one sender using that IP address, all the senders on that server could get blocked.

Also, validating the IP address doesn’t legitimize the messages coming from it. Spammers often hop from one IP address to another to avoid detection. So, you need another layer of authentication to separate good and bad senders.

 However, domain-level authentication doesn’t address message content, either. That leads to another factor that receivers add to the decision-making mix: engagement.

Further, ISPs look for positive user actions like these:

ISPs don’t judge your message quality. Rather, they take their cues from their users. Senders whose messages have higher user activity are more likely to hit the inbox.


  1. Three things that make email receivers think your messages are spam

Although each ISP has its own algorithms or decision-making formulas, some activities are considered universally spammy:

At one time that meant having content that filters associated with spam, such as using “free” in the subject line or “click here” in the copy. A few email receivers still use keyword filtering, but the major ISPs consider elements such as using third-party links in your messages or using nonstandard HTML coding or formatting.

The problem with third-party links is when they go to dicey websites, such as aggressive third-party acquisition sources or those known to trick visitors into downloading malware. Instead, use your own link and redirect to your partner site after you vet it carefully.

  1. Best practices to stay out of the spam folder

Play by ISP rules as best you can:

 It is now required by most email laws around the world to get permission. But, even if your country’s laws permit opt-out, your recipients and their preferences are your most important consideration.

Reach out to your silent subscribers through a reactivation program or change the way you send to them. The actual amount of time will vary with your customer lifecycle – you might need more time if you sell luxury or lifetime purchases or less if you sell everyday products.

Staying out of the spam folder is paramount. For a more in-depth guide to understanding the key challenges that impact deliverability and how to overcome them, download our latest eGuide, Understanding and Addressing Email Deliverability.  

deliverability e-guide 2016

You’ll be thankful you did!


John Stephenson is Head of Deliverability at Adestra.