North Star deliverability metrics for your email program

We talk a lot about email deliverability at Mailgun, but which metrics will guide you best to understanding and improving your email strategy? Keep reading and we’ll show you how to monitor deliverability metrics like a pro.



There are 100 billion stars in our galaxy alone, but we bet you can only call out a few by name. Likewise, you can get incredibly granular – even microscopic – when it comes to tracking metrics, but sometimes it can be hard to analyze all the data points connected to your email program.

So, we’re breaking down the mission into two stages: delivery and engagement. Do your emails get into the recipients’ mailbox? If so, how are your users interacting with your messages and how does that impact your deliverability?

Metrics aren’t just email marketing tools – they are key indicators of an email program’s overall deliverability. Which points will guide your strategy? We’ve got the answer.

How can you know if you’ve got a strong email deliverability?

We get it, email deliverability is complicated. You might be seeing low open rates or low conversions from email, but you don’t know the cause. Or maybe you’ve just heard it’s important to have good deliverability, but have no idea how to track it, or solve for any problems. Don’t get frustrated. Deliverability is a complex topic.

We can start to break this down by looking at factors that contribute to a strong deliverability program:

  • Email address list health: A clean, validated email list helps mitigate failures from hard bounces, and ensures that the addresses not only exist, but that the users intended to subscribe. A clean list improves open rate while reducing complaints.

  • Strong engagement: ISPs will determine inbox placement by a number of factors including engagement. Open rates, complaint rates, and unsubscribes all contribute.

  • Following best practices for reputation building and security: To land in the inbox you can’t be mistake for spam. Authentications like SPF, DKIM, and DMARC are the first step to a good reputation.

If we had to boil deliverability down to one thing, it would be sender reputation. Take it from our deliverability pros. According to Kate Nowrouzi, VP of Deliverability at Mailgun, monitoring your email deliverability is important for several reasons including reputation management. Email service providers and ISPs such as Gmail, Yahoo, and others use your sender reputation to determine whether to deliver your emails to the inbox or to the spam folder. Poor email deliverability can damage your sender reputation and lead to your emails being blocked or filtered into the spam folder.

“Poor email deliverability can damage your sender reputation and lead to your emails being blocked or filtered into the spam folder.”

Kate Nowrouzi VP of Deliverability at Sinch Mailgun

Email delivery metrics to know and track

What are delivery metrics, and how are they different from other email deliverability and marketing metrics? The answer depends on who you ask.

Delivery metrics are data points you can track to ensure your message has been delivered. Before messages can even get to your user’s inbox or spam folder, emails need to make it all the way to the recipient and be accepted by accepted by their mailbox provider. Delivery metrics track if this is successfully happening.

Email delivery metrics include:

Delivery rate

Your delivery rate has two parts, acceptance and delivery. Acceptance is when your email service provider (ESP) has accepted the request to send the message and has placed it in the queue. This is worth looking at separately if you are having issues with your deliverability, which could range from a storage issue to an outage.

Delivery happens when the recipient email server has accepted the message and as a whole can be calculated by dividing the number of successfully delivered emails by the number of emails you sent.

Bounce rates

Knowing your email bounce rates, and their causes, is mission-critical for your delivery with one caveat. When it comes to bounces in terms of delivery, what you’re really looking at are failures. “Bounces” can mean a lot of different things in the email industry, so we typically communicate these metrics as failure rates, which are attributed to causes like a blocked IP, bad reputation, and bounces (for us that means a delivery failure because an address doesn't exists).

  • Hard Bounce: A permanent delivery failure caused by an invalid email address, or when the sender’s IP or domain is blocked by ISPs.

  • Soft Bounce: The message has failed due to a temporary outage or resolvable issue.

The recipe for reducing bounce rates is fairly simple. Keep your email list clean by verifying your addresses regularly for good list management. Don’t ever purchase email lists, as these addresses haven’t given permission to receive your emails which can increase your likelihood of being labeled as spam.

These are the most critical metrics to monitor in terms of just delivery, and we could stop there. But metrics don’t end with arrival. If we view email metrics as data points along a message’s journey, it’s clear that these metrics only give you the full picture when they are combined. So, let’s look at what happens next.

The best email engagement metrics to track

After delivery we’re going to look at metrics that impact engagement (a major factor that contributes to your deliverability) how to create engagement, nurture it, and establish an end goal for users when they interact with your content. These are the four we have our eyes on:

Open rate

Your open rate is the percentage of recipients that open your email, and you find it by dividing the recipients by the number of opens. An important call-out to make here is that bounced emails don’t lower your open rate percentage. Your open rate is your first glimpse into your engagement, but it can tell you so much more.

Open rates tell you the percentage of emails you sent that were actually opened by the recipient. They give you an idea of how well your emails are being received and how strong your sender reputation is, and how effective your subject line is at encouraging people to open your emails.

However, open rates are not a perfect metric and have some limitations. They can be unreliable due to various reasons:

  • Email clients display images by default: Some email clients display images by default, and the open rate is calculated when the images are loaded. This can lead to inflated open rates as the recipient may not have actually read the email.

  • Privacy settings: Some recipients have privacy settings that block images from being loaded, so even if they've opened the email, the open rate won't be recorded.

  • Email filters: Spam filters and other email filters can prevent emails from being delivered, which will affect open rates.

  • Inaccurate tracking: Some email tracking software may not accurately track opens, leading to under-reported open rates.

Overall, while open rates can provide some valuable insights, they should be used in conjunction with other metrics and data to get a complete picture of email deliverability and effectiveness. Additionally, it's important to keep in mind that open rates can be inflated or under-reported and should be interpreted with caution.

“While open rates can provide some valuable insights, they should be used in conjunction with other metrics and data to get a complete picture of email deliverability.”

Kate Nowrouzi VP of Deliverability at Sinch Mailgun

Assuming that your sender reputation is on point, your deliverability is high, and your inbox placement is prime – you still have to compete with a sea of marketing emails. To stand out, we recommend obtaining your brand indicators for message identification (BIMI) certification, which showcases your company logo in the inbox, or even just showcasing your logo by adding a sender image.

Click-through rate

You’ve gotten your recipients to open your emails, now you have to get them to interact. Your click-through rate is the percentage of people that click at least one link within your message. In other words, this rate measures the effectiveness of your link placement and messaging, and the percentage of recipients that are interacting with your email after they open it.

Getting someone to click on a link within an email can be a bit like getting a cat to walk through a door. The cat meowed, you opened the door, the cat ignores you… until you dangle a treat in its face. Recipients click on links when they’re interested in the content and find it valuable enough, or are intrigued enough, to want to learn more.

You want your click-through rates to be high on your transactional emails as well, which boils down to clarity. Sending a triggered email for account cancellations? (We hate it too, but it happens). You better make sure that cancellation process is easy when the instructions are sent. We won’t linger on the subject of cancellations though, let’s move onto subscribers.

Subscriber list growth rate

Your list growth rate factors in two data points, your new subscriber rate and your unsubscribe rate. The relationship between these two metrics can tell you a lot. If you have a low list growth rate you need to start asking questions. Did you put out a promotion for a discount with sign-up and then subsequently lose subscribers after they redeemed? Are you blasting your lists with messaging? Do you have double-opt ins in place to ensure those on your list actually want to subscribe?

Unsubscribe rate

The unsubscribe rate, as we’ve just mentioned, goes hand-in-hand with your list growth rate, and is simply the rate that your recipients unsubscribe. We’ve name-dropped a few reasons why your unsubscribe rate might be high. Let’s focus in on them a little more.

  • Unengaged lists: Create a segmentation strategy to isolate inactive or disengaged users from your email lists. And then either implement a separate campaign geared toward reengagement or develop a sunset policy to remove inactive emails to keep your list clean and optimized.

  • Campaign schedules: Don’t inundate your recipients with a ton of email campaigns. There’s a sweet spot between nurturing engagement and being annoying.

Complaint rates

Out of all the actions that can lead to your emails landing in the junk folder rather than the inbox, high complaint rates might be the most decisive factor. The complaint rate is the number of people that receive your email and complain by marking it as spam.

ISPs pay attention to user engagement when deciding on inbox placement. This makes the complaint rate particularly enlightening. If your recipients are marking you as spam then you either are spam, look like spam, or your content is not helpful or well-received. The truth isn’t always pretty, but this metric can be your mirror when looking at the influence of your messaging.

You can poll for recent suppressions like bounces, unsubscribes, and complaints in your Mailgun account using our API.

Final thoughts

This is not a short list of metrics, but by breaking your email program apart for analysis – and then zooming out to look at it from a macro level – it’s easier to identify the few key data points in each phase that give you impactful information across your email program as a whole.

Whether you’re analyzing campaigns, or looking at the effectiveness of your transactional emails, these metrics not only matter, they act as spotlights that showcase how and shine a light on potential areas of improvement.

Was this content interesting and helpful? As you can tell, we love to talk about email. We also love to help you implement effective deliverability practices. Our technical account managers know all the ins and outs so you don’t have to navigate blindly.

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