Post: deliverability | Aug 22, 2022

Email deliverability: It’s not as difficult as you think

By Andrew Bonar, emailexpert.

Industry insiders will often talk about the differences between delivery and deliverability of emails. For the most part, you can have great delivery and poor deliverability, but you cannot have poor delivery and great deliverability.

Let’s dive deeper into these two concepts. Simply put, delivery is the common definition of getting your email accepted by the recipient's MTA. Deliverability on the other hand is commonly used when discussing how your email is accepted into the intended recipient's inbox. In other words, deliverability can not happen without delivery first. 

To have good deliverability you need good delivery. In comparison to deliverability, delivery is to a greater extent where many of the difficult things happen. For this reason, it’s important to follow some essential delivery rules.

  • Connect to the receiving MTA at the right speed and frequency
  • Send from IPs that are correctly configured
  • Properly configure the domain names associated with the email
  • Ensure the email envelope and content is compliant with relevant RFC’s
  • Authenticate the email in a correct way.

The points above are simplified - each bullet-point could be a blog post or even a book on its own. However, broadly speaking, these are the most significant points and all of them are fundamentally important aspects to get technically right. Also, not everyone controls this in-house. Some email marketers delegate the entire responsibility of this to their Email Service Provider (ESP). Who will in turn manage some or all of this through an MTA, such as the Halon MTA. 


Whilst some will prefer outsourcing to ESPs, others will look for greater control around how their email is delivered by managing their Halon MTA in-house. By doing so, they take on the responsibility for the harder aspects of delivery, like per-ISP delivery settings, IP management, abuse mailbox management, feedback loop registration, bounce management rules, message headers and similar. These aspects of outbound sending and MTA management are areas that organizations like Halon and other specialist MTA’s can support. 

If you have got all that technical stuff right, are sending relevant and permission-based emails, and running your operations on a reliable MTA like Halon, then we can assume good delivery. If you have not got your configurations correct or fail to authenticate properly, you can find that your email is outright rejected by the receiving MTA. 

There is one area in which factors are related to deliverability and that can impact delivery significantly. This is connected to the permission from recipients for the emails being sent, or more accurately - a lack thereof. If a sender does not have relevant permission from the recipient, then you can quickly find all emails from that sender being blocked. 

I have always said email deliverability is not rocket science, or even as difficult as you think. The technical matters are almost exclusively a matter of delivery. Deliverability is primarily a matter of permission, value, relevance and accessibility. Long ago when I was asked to define deliverability, I said “deliverability is the art and science of getting your message seen by the intended recipient, in the way it was intended, where and when you intended it to be seen.” 

I believe that is as true today as when I first said it around 20 years ago. Comparing that time with today, not much has changed in terms of the factors that will impact your deliverability. With that said, it is the same issues that can have the biggest negative impact on your deliverability today as it was then. The way in which we measure these factors may have changed but fundamentally, they are still the same: 

  • Invalid recipients 
  • Complaints
  • Low engagement
  • Content: structure and formatting

In and of itself - none of the above is hard. Yet, none of us live in a perfect world. Whilst properly ensuring you have permission to send emails (confirmed opt-in; COI), you will mitigate the issue of invalid recipients, as well as send emails that are expected and you have given permission for, which will minimise complaints. Providing relevant content that is of value and of interest to the recipient will make certain you maintain good engagement rates with your emails. 

In terms of content, we long ago stopped worrying about trigger words that will get the email sent to junk. However, formatting still matters, especially when it comes to “how you intended your message to be seen”. The issue of your content being formatted correctly is a matter of testing your message against the various email clients to ensure the message renders as expected. This includes guaranteeing your email is accessible to those using screen readers, the color blind and others.

The key to getting all of this right lies in the execution. This is where the deliverability fun but also the challenges begin. The reason we care about deliverability is because of its ability to push the needle in terms of the return-on-investment (ROI) from the email channel. In this way, 100% deliverability is not only an extremely unlikely ideal to ascribe to, but it is rare that 100% deliverability is your goal nor the true KPI in measuring your success with the email channel. 

Whilst none of this is brain surgery, when running mission critical or complex email messaging channels, having a good deliverability expert on call is invaluable. Communications leaders, marketers and others do not work in an ideal world and issues do occur. A good deliverability expert will help you navigate ways in which to mitigate inbox placement issues, complaints, low engagement and email rendering problems. Moreover, they will help map an approach that secures that you meet your messaging goals (marketing, transactional, compliance or otherwise) whilst maintaining optimal deliverability.

About Andrew Bonar

Andrew Bonar, senior advisor to the Halon executive team, started in email over 25 years ago working on the receiver side as Co-founder of the British mailbox provider and ISP @Pobox before going on to found one of Europe's earliest ESPs. Over the course of his career in email he has worked with ESPs and MBPs across Europe, China, North America and Australia. He has consulted for organizations including Amazon Retail, SES, Kogan and DotDigital amongst others with difficult delivery and deliverability challenges as well as heading up global deliverability for a variety of ESPs in his career including Emailvision, SmartFocus and Campaign Monitor.

Andrew now publishes the website emailexpert, is a frequent speaker at industry events and organiser of the Inbox Expo and Deliverability Summit conferences.