Craig Sully, Purlos’ Product Operations specialist set out to increase Purlos’ email deliverability from 79% to as close as 100% as possible. He noticed this low rate of deliverability after our email channel opened, as our emails only hit 90% of inboxes, and then at the end of December, this dropped further by another 11%. This was alarming, as it led to us capturing fewer Destinations. For those who don’t know, Purlos uses emails to learners as a channel for chase ups for our Destinations capturing messages, when WhatsApp and SMS fail. Here’s his journey from his point of view, but first; for those who aren’t aware – what is Email Deliverability?


In short, email deliverability is the ratio of delivered to bounced/invalid emails. The more emails you are able to deliver to a mailbox, the better your sender reputation will be – this is reflected on the IP you are using to send the emails. If your emails are constantly landing in the ‘Spam’ or ‘Junk’ folder, your reputation will decrease drastically. If your reputation continuously drops, your IP will be automatically blocked and your emails will no longer be received by your intended recipients. So, keeping a strong sending reputation is crucial when sending emails in bulk.


We started to A/B test different variations of the subject line, and also the email contents. Our aim was to make the email as credible as possible, to safely deliver our emails to the intended recipients mailbox, without the provider having any concerns. We tried a myriad of different emails, with some success, but not enough. By the end of January, we had improved our deliverability to 84%. So my first thought was, well what is a good deliverability rate? After some thorough research through various marketing data sites, the industry-standard deliverability rate was 95%. Clearly, we were steps behind…


Next, I wanted to deep dive into the problems. Why are 16% of our emails not being delivered? The overwhelming majority of blocked emails were using the mailbox provider, Microsoft Outlook. So, my next mission was to find their criteria to ensure our emails met their standard. After consuming as much information on the topic as humanly possible, it seemed like Microsoft Outlook was a problem for many bulk email senders. 


As we were ramping up our email sending to be capable of handling more volume, we upgraded our package with the email sending software. As a byproduct of this, it gave me access to every single failed email and the reason for the failure. After individually checking the hundreds and hundreds of failed emails, I had found the root cause of our problem. Our shared IP had been blacklisted by Microsoft Outlook. This meant that regardless of our email content, any emails being sent to a Microsoft Outlook mailbox would be automatically rejected. 


As a result of the software upgrade, we now had access to a private IP and consequently, we were no longer blocked by Microsoft Outlook. Problem solved right? Not quite. Firstly, we had to warm up this new private IP by sending a maximum of 28 emails per hour for roughly 4 days. This proves that we are not planning on using the IP for spam or anything with malicious intent. Once the warm up was complete, we started to see the fruits of our labour. Our deliverability had risen from a measly 84% up to 91%. But this wasn’t good enough…


The most commonly rejected emails are to users who have a full mailbox or to emails that no longer exist. If a human looks at an email, there is no way to tell if that mailbox is full. Also, if there are no glaring typos, we cannot detect whether the email address exists. So, my research expanded from marketing data sites, to email validation sites. After trialling a variation of different sites, we landed with one known for its quality over quantity; ZeroBounce. The software could identify (in bulk) whether or not an email address was valid – and report back on the reasons for the invalid ones. The initial tests on this software were promising, so I wanted to see if it could handle more volume. Time after time, it continued to impress me with its accuracy achieving an accuracy of 99.9%. 


We integrated this validation into our email sending process, to exclude all invalid emails before they are sent. This has now led us to the present day, where we constantly achieve a deliverability rate of 99%+, with the last month achieving 99.6% across thousands of emails. We now have a very strong sender reputation and an almost guarantee that all emails will be delivered to contacts mailboxes. 


This 3 month long process has had one aim in mind: To capture more destination codes. In comparison to the start of our email sending, we are now reaching over 20% more mailboxes which means more potential destinations.

So why not try increasing your own Email Deliverability? Or if you’re interested in reaching 99.9% of students via email and potentially collecting their destinations – book a demo here.

Amber Cousins