How we improve email deliverability at PayStack

The 1 Line Description

A detailed breakdown of how we significantly improved our deliverability and sender reputation.

When to use it

From the first mailing campaign.

Key Ideas

*This article contains direct excerpts from this PayStack blog post. Thank you to Paystack for their willingness to share their content, to help grow the ecosystem.

In late 2018, a friend sent me a screenshot of a warning he received from Gmail when he opened an email broadcast from Paystack - a large yellow banner carrying the words “Be careful with this message.”

Gmail warning an email recipient about a Paystack email

Gmail was warning our email subscribers that our emails might be harmful, and it was immediately clear that our open rates and email deliverability could suffer as a result.

In this article, I’m going to share in detail everything we learned while fixing this. If you're ever in a similar situation, this post should help you resolve it for yourself.

Understanding Email Sender Reputation

I did several Google searches to understand the problem, and quickly realised that:

  • It was hard to find a single guide that explained everything I needed to do from A to Z
  • Email Sender Reputation significantly influences email deliverability

An Email Sender Reputation is a score, usually between 0 - 100, that Email Service Providers (ESPs) such as Gmail, Outlook, and Yahoo Mail assign to organisations that send out emails. The higher the score, the more likely it is that ESPs will deliver emails to subscribers’ inboxes.

The lower the score, the more likely it is that when you send broadcast emails, many of those emails will either get caught in subscribers’ spam folders, or not get delivered at all.

We monitor our reputation score with Sender Score's look-up tool. Check your email sender reputation.


An Email Sender Reputation score is a score assigned by Email Service Providers such as Gmail and Yahoo Mail to email marketers. The lower the score, the more likely your emails will end up in spam.

A lot of factors contribute to the reputation score, but the important ones all have to do with how subscribers engage with your emails. ESPs listen for both positive and negative engagement signals to increase or reduce a sender’s reputation score.

Examples of positive engagement signals include:

  • a high open rate - your open rate is the percentage of people that open your email compared to the number of people who received the email
  • a high click-through rate - the click-through rate is the percentage of people who click on a link in your email, compared to the number of people who received the email
  • subscribers forwarding your emails to other recipients

Examples of negative engagement signals include:

  • a very low open rate
  • subscribers reporting your emails as spam
  • a high unsubscribe rate
  • inclusion of your domain name in email blacklists (more on email blacklists later)
  • a high hard bounce rate - the percentage of emails that don’t get delivered because they were sent to invalid email addresses
  • a high soft bounce rate - the percentage of emails that don’t get delivered because they were sent to subscribers with full inboxes

A checklist for improving your email deliverability and sender reputation

Here’re the actions we took to improve our Email Sender Reputation, and by extension, our deliverability. We'll dive into each one in detail.

  1. Authenticating Paystack’s email sending domain
  2. Removing Paystack’s domain from credible email blacklists
  3. Periodically pruning our email list of hard bounces
  4. Monitoring key email deliverability metrics