How to Diagnose an Unexpected Drop in Open Rates and Engagement

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“We saw a drop in open rate and engagement recently, and we’re not sure what’s going on. What are the steps you’d take to diagnose the problem?”

Deliverability is a complex topic, and sometimes, things can go wrong — open rates drop, engagement dips, and you’re left wondering, What happened? Don’t panic. Drops in engagement happen to even the best of newsletters, and the good news is there are several steps you can take to diagnose and fix the issue.

First off: If a single email suddenly has a lower-than-expected open or click rate, that might not be a sign that you have an issue. Maybe the subject line or content didn’t resonate with readers, or maybe the inboxes filtered your email to an unexpected folder. Those are often one-off issues and not signs of a larger issue. Send a few more emails and see if things revert to normal — they often will.

But if you start to see a long-term drop in engagement, there might be a bigger issue at play. In this guide, I’ll walk through a checklist of things to investigate when you see a decline in your open rates or engagement, and I’ll explain how to tell if it’s related to your sender reputation and deliverability.

1.) Double-check your sender authentication settings

One of the first things you should always check is your DNS entries. These entries (SPF, DKIM, and DMARC) are the backbone of your email authentication. Even if they were set up perfectly before, things can change — your email service provider, or ESP, might have made updates, or someone might have accidentally altered or deleted an entry. If your authentication is broken, inbox providers like Gmail or Yahoo will have a harder time trusting your emails.

It’s easy to miss notifications from your ESP about these changes, so make sure to monitor your DNS settings regularly. Setting up alerts can help you catch these issues before they affect your deliverability.

2.) Check your DMARC reports

DMARC reports are invaluable in helping you see if someone else is sending emails using your domain without your knowledge. Even if you’ve set up SPF and DKIM, some senders configure DMARC to pass if only one of those checks passes, which leaves room for bad actors to impersonate your domain.

By reviewing your DMARC reports, you can catch issues early. To make it easier, you can use tools like EmailConsul’s DMARC Analyzer, which helps you interpret those tricky XML files in a more readable way. 

If your DMARC also looks like this — v=DMARC1; p=none; — your domain is not actually protected from those who might try to impersonate you. (You need to have your DMARC set to p=quarantine or p=reject to stop those bad actors.) We’ve got step-by-step instructions here to talk you through the process, or you can register with a free service like Let’s Authenticate the World to get more hands-on help in setting up DMARC.

3.) Monitor your reputation (and check subdomains, too)

Your sender reputation can give you crucial insights, even if it doesn’t provide all the answers. Use tools like Google Postmaster, SNDS or Yahoo’s Sender Hub to monitor your sender reputation. Any dips, even if temporary, could indicate spam complaints, bounces, or issues with a specific campaign that needs further investigation.

Also, check whether you’re sending from a subdomain or root domain. (If you’re not quite sure what that means: A primary domain would be something like inboxcollective.com, while a subdomain might be mail.inboxcollective.com.) Subdomain deliverability can be affected by the root domain’s reputation, so it’s important to make sure both are properly being monitored, configured, and healthy. 

4.) Check the basics: Lists, segments, and recent changes

Before diving too deep, take a step back and ask yourself: Have there been any recent changes you’ve made to your email strategy? This might include:

• Uploading a list of new subscribers to your ESP or sending to new segments of subscribers.
• Emailing recipients who haven’t heard from you in a while.
• Making big changes to one of your email templates.
• Turning on new automations in your ESP.
• Significant growth in the size of your email list.
• Adding a new sender domain or subdomain.
• Suddenly promoting different URLs than what you usually promote, or adding new link tracking to your URLs.

Unexpected changes can catch the attention of the inboxes — their filters might be suspicious if they see new behavior from a sender, and that might cause them to throttle your emails or send mail to spam. The good news is that the inboxes are very smart, and they tend to adjust quickly to new behavior — as long as you’re a legit sender who is following other best practices.

One more thing to note: There are moments when filters are on high alert for spammy behavior. During the pandemic, for instance, there were significant spikes in email scams, and the inboxes adjusted to try to keep readers safe. But those filters sometimes filter legitimate emails to the spam folder.

When spam filters are on high alert at times like these, senders may be confused when the open rates fluctuate. You might not be doing anything wrong — it’s just the result of changes from those filters or security bots. The humans on your list are opening and clicking at the same rate as before, but the drop in bot activity might make it seem like there’s a larger issue at play. (There isn’t, don’t worry!)

5.) Have the inboxes announced any recent changes?

Internet Service Providers, or ISPs, include mailboxes like AOL, Gmail, Outlook, and Yahoo. They don’t always publicly announce updates, but they frequently adjust their algorithms to combat spam, which can affect your deliverability. For example:

• If ISPs start prioritizing engagement, senders who aren’t regularly cleaning their email lists might see their emails fail to land in the primary part of the inbox.
• If authentication becomes more important, senders who were skating by without SPF, DKIM, or DMARC set up properly may suddenly find their emails being blocked or sent to spam.
• If a specific scam triggers changes to spam filters, and if your content accidentally resembles that spam, you might find your emails being sent to spam.

Monitoring industry trends and staying informed can help you adapt to these changes faster. Industry blogs, like Badsender or Spam Resource, can be invaluable for staying on top of these trends.

6.) Investigate if you might have been greylisted

Some ISPs practice greylisting, which is when a piece of email is temporarily rejected because the inbox thinks it might be spam. The ISP is saying, “This mail can’t be delivered now — but try again later.” Your ESP will try again to deliver your mail based on the automated rules they’ve put in place regarding individual types of bounce messages they receive from ISPs.

This practice helps ISPs cut down on spam, but it can also delay delivery of your emails. You can check with your ESP to make sure they’re trying to deliver emails again so your messages aren’t left in a state of inbox limbo.

7.) Check if there are any issues with your ESP

Occasionally, the problem might not be on your end but with your ESP. These email platforms are typically pretty quick to fix any issues, but even a temporary hiccup could cause problems with email delivery or data. In some cases, you’ll find that there’s no issue with your newsletter — the problem is that your ESP suffered a temporary server issue, and your data just hasn’t shown up in the campaign report yet.

Nearly every ESP offers a status page where you can see if there are any issues, like https://status.beehiiv.com or https://status.mailchimp.com. (Adding “Status.” before your ESP’s website is usually a good way to find the right page.) 

You can also check with your ESPs customer service team to see if they can shed any light on behind-the-scenes issues. For instance, if you’ve moved from a shared IP to a custom IP, it’s possible there was an error made in the migration process. That’s something your ESP should be able to help you investigate and correct.

8.) Run inbox placement and blocklist tests

One of the most direct ways to check your deliverability is through an inbox placement test. This helps you see where your emails are landing (inbox, spam, or nowhere). There are free tools, like ones from EmailConsul, Glock Apps, or Gmass, that can help you do this. (There are also paid tools, like Inbox Monster or Everest, that offer more robust monitoring.) By tracking your inboxing rates over time, you can be notified when something starts going south. But these tools aren’t perfect — they track a variety of inboxes, but each reader’s inbox is different, and an email that lands in the spam folder for one reader might land in the primary inbox for another. Use these tools alongside other email metrics to better understand what’s really happening. 

Along with this, some inbox placement tests allow you to check if you are authenticated properly and also check if your IP addresses or domain are on any DNS-based blocklists, or DNSBLs. Not all blocklists are created equal. Some, like Spamhaus, can have a huge impact on deliverability, especially on Microsoft emails, while others, like UCE Protect, may not affect your inboxing much at all based on who is on your list and the inboxes you are sending to. (It’s possible to get off a blocklist — here’s how to do that for Spamhaus, for instance.) Regular inbox placement tests can help you stay on top of any potential blocklist issues.

9.) Check for a few unexpected errors

There are a lot of little things that might be causing the drop in engagement. For instance: Maintaining a clean list is crucial, but there are so many points of failure that even the most careful senders can face issues. Maybe you:

• Send to an old list that should have been archived.
• Forgot about a form that might be feeding spammy subscribers onto your list.
• Haven’t set up an opt-in strategy that keeps your list clean.
• Uploaded inactive lists or segments that haven’t been emailed to in a long time.

There are many things that can go unnoticed. For example, if your emails have been going to spam for weeks, and they suddenly resolve, some readers might start getting your emails for the first time in a while. That’s usually a good thing — but you might also see spam complaints from readers who forgot about you or no longer care about your content. These complaints can hurt your reputation and cause further drops in open rates, even though you’ve technically fixed the initial deliverability problem.

You also may want to look at spam complaints based on domain. An issue with spam complaints may start with an inbox provider that only represents a small percentage of your list, but as you acquire more readers on that ISP, the issue may become a bigger deal down the road.

I also like to use UTMs to compare clicks tracked by an ESP with those tracked by a website analytics platform, like Google Analytics or Fathom Analytics. This helps me spot differences between human and bot clicks. It’s also helpful to create baseline metrics for success, so if things start to change, I’ll spot that something looks off, and then I can work to fix issues quickly.

Finally, remember that segmentation can cause issues, too, especially for newsletters with massive lists. Sending to a list of highly-engaged users, for instance, is typically a smart strategy, but what if a disproportionate number of them are Yahoo users? A sudden spike in emails to that one ISP might cause some problems, and you may need to break those segments into even smaller lists to avoid potential problems.

10.) Review your bounce data

Bounces are more than just failed deliveries — they tell a deeper story about your list’s health. Many senders think hard bounces are only due to full mailboxes or non-existing addresses, but they can often signal more serious issues. For example, a hard bounce might indicate that an email was blocked by an ISP due to suspected spam. These types of bounces are warnings that your sender reputation could be in jeopardy, and they’re also a flag to help you figure out which ISPs are the ones you need to deal with.

It’s crucial to monitor bounce messages closely — most ESPs will share data with you about these bounces. Inboxes sometimes provide valuable feedback through what’s known as “bounce codes,” such as “blocked due to spam-like content” or “too many complaints from this domain.” Ignoring these signals can lead to broader deliverability issues.

Pay special attention to whether your bounces are concentrated around one or two ISPs. If a large percentage of your bounces come from just one ISP (i.e, just Yahoo), it could mean you’re facing specific issues with that provider. This may be due to content triggers, reputation issues, or list hygiene problems that are more sensitive to that ISP’s spam filters.

Regularly reviewing bounce data, especially by ISP, can help you uncover and fix targeted deliverability problems before they spread to other inbox providers.

11.) Check your automations and transactional emails

If a significant portion of your list is disengaged, it can drag down your sender reputation. Reactivation campaigns are a great way to win back inactive subscribers or remove those who are no longer interested. The more engaged your list is, the better your deliverability.

However, reactivation campaigns can go wrong if they run too long. (Think: Weeks or months, not days.) If uninterested subscribers keep receiving these emails without engaging, it can lower overall engagement rates and further harm your sender reputation. It’s important to carefully segment your re-engagement efforts and regularly review those segments. Adjust the content, timing, and cadence based on how subscribers are responding. Only those with a real chance of re-engaging should continue receiving these emails — there’s probably very little good in emailing a reader who hasn’t opened in three years and trying to get them to come back — while the rest can be cleaned from your list.

Automations are incredibly powerful, but they can be easy to overlook once they’re set up. The problem often starts when we set and forget automations. If you’re not checking these automations at least a few times a year, you may find that they lose their relevance. Your audience might have grown or changed, or different segments of your list might now want different things from you. What once worked well might now feel out of touch, or even annoying, to these readers.

It’s important to audit your automations periodically. Are they still relevant? Are they serving your audience’s current needs? Are you sending them to the right people and at the right cadence? The key is to make sure that automations remain aligned with your audience’s current expectations and don’t inadvertently push subscribers away.

Lastly, it’s important to audit your transactional email strategy. Transactional emails are emails that need to be sent because a user initiated an action, such as a password reset, purchase receipt, or account confirmation. These emails are critical because they fulfill a direct user request.

There’s often confusion about what qualifies as transactional. For example, some ESPs or marketing teams might label an abandoned cart email as transactional simply because they’re sent through an automation feature or by API. However, I wouldn’t classify abandoned cart emails as transactional — they’re marketing emails, and should be treated as such.

Treating marketing emails as transactional can create deliverability issues. Transactional emails typically bypass certain filters, but if you abuse this by labeling marketing content as transactional, you may end up harming your sender reputation in the long run.

12.) Monitor for spam traps

If your engagement suddenly drops or you see a spike in complaints, you may have spam traps in your list. These traps are designed to catch senders with poor list hygiene — they’re fake email addresses that blocklists use to identify readers who might be buying email lists or engaging in shady practices, and having traps on your list can cause serious deliverability problems. Regularly using list validation tools, like Bouncer or Kickbox. can help keep your list free of traps.

What to do next

Diagnosing a drop in open rates and engagement can feel overwhelming, but taking a methodical approach will help you identify the root cause. By working through this checklist, you’ll be able to pinpoint potential issues and make the necessary adjustments to improve your deliverability.

Sometimes, it helps to bring in a fresh perspective. Talking to a deliverability specialist can be invaluable — they may spot something you’ve overlooked or help you analyze results more effectively. (You can always reach out to Dan for suggestions.) They can also speak with your ESP on your behalf to dig deeper into potential issues by helping you ask the right questions.

Remember, it’s important to be honest with yourself. What worked before may not work now. Spam filters, blocklists, and security measures are constantly evolving to catch new threats, and things that didn’t matter in years past might become critical now. While it can be frustrating to adapt, it’s also essential for maintaining a healthy email program.

If something isn’t working, take a step back and reevaluate. Staying proactive is the key to keeping your emails out of the spam folder and delivering the results you need.

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