A practical guide to inbox delivery: The path to the heart

The path to the heart of an inbox.

If you didn’t read the first part in this series, or you skipped it, we introduced you to the history of why email delivery became tricky, and how this guide will help you to deliver email to the inbox.

So if in the late ‘90’s the email industry was a cowboy frontier, the West has since been won, and the pace and complexity of life has caught up a little. When you send an email to someone, its important to understand that there is both Inter-ISP differences as well as Intra-ISP differences that affect delivery. This means that inboxes have individual tastes of why email they think of as good, and they learn this from which emails you open, complain about, or delete.

  • Inter-ISP difference means that not all ISPs evaluate email in the same way. This means that a mail be inboxed by Gmail, while getting junked by Yahoo. The basic lesion is that there is no universal junk mail indicator. We’ll get into the reasons why later.

  • Intra-ISP difference means that ISPs themselves prioritize mail differently per user. For example, if a user has a history of opening mail from an IP that has a poor sender reputation, many ISPs will inbox mail from that IP for that user only while sending it to junk for the majority of users. This practice began around 2010, and is broadly called “Engagement monitoring” which is covered in later in this series.


So how does one operate in an environment where there is such unforgiving variability? Luckily, the answer is not that you need to consider every single variable that affects your subscribers. Rather, the myriad factors of email delivery are generally dictated by the following simple high level checklist, which can be applied to context fairly easily.


  • Where do subscribers come from, and how do they get onto your list?
  • What do you send to them?
  • How do you code it?
  • How often do you send it to them?


There are several sub sections under each of these factors. The next article in this series will deal with those under “where do your subscribers come from?”.

If you have any specific questions after reading this, our delivery team responds to them within 24 hours, so hit us up here