What causes a sudden drop in email open rates and emails landing in spam?

A sudden drop often points to issues with sender reputation, which can be affected by factors like increased spam complaints, high bounce rates, low engagement, or being listed on a blacklist (or blocklist) . Technical misconfigurations in SPF, DKIM, or DMARC can also cause emails to land in spam, thus impacting open rates. Changes in content quality or list hygiene can also play a role.

How can I diagnose the specific reason for the drop?

Start by checking your core email metrics, especially spam complaint rates and bounce rates. Verify your email authentication (SPF, DKIM, DMARC) are correctly configured. Use tools like Google Postmaster Tools for Gmail insights and analyze your DMARC reports for detailed delivery data. Evaluate recent changes to your sending infrastructure or content strategy.

Could a shared IP address be causing my emails to go to spam?

If you're on a shared IP address , the sending practices of others using the same IP can affect your reputation. While a shared IP is sometimes the cause of deliverability issues , it's not always the primary culprit. Focus first on your domain's reputation and your own sending practices, as these often have a more direct impact.

Can seasonality affect email open rates and make emails land in spam?

Seasonality can certainly impact open rates, especially for audiences whose email activity fluctuates with specific times of the year (e.g., educators during summer breaks). Compare current open rates to the same period in previous years to determine if the drop is part of a normal cycle or an anomaly indicating a deliverability problem. If the drop is more significant than usual, other factors are likely at play.

How to diagnose sudden drops in email open rates and emails landing in spam? - Sender reputation - Email deliverability - Knowledge base

A sudden drop in email open rates and a surge in emails landing in spam folders can be a distressing experience for any sender. It indicates a significant problem with your email deliverability, potentially impacting your engagement, conversions, and overall sender reputation. This isn't just a minor blip, it's a clear signal that something fundamental has changed in how mailbox providers are perceiving your emails.

The challenge lies in pinpointing the exact cause. It could be due to a myriad of factors, ranging from technical misconfigurations to changes in your sending behavior or recipient engagement patterns. Understanding where to begin your investigation is crucial to quickly mitigate the damage and restore your email program to health.

Initial checks and data analysis

When facing a sudden decline in open rates or an increase in spam placements, the first step is to methodically review your email metrics and sending environment. Your email service provider (ESP) typically offers dashboards with basic statistics, but a deeper dive is often necessary. Pay close attention to trends, not just isolated numbers. Did the drop happen suddenly on a specific date, or has it been a gradual decline?

It's also important to differentiate between an IP reputation issue and a domain reputation problem. If you're using a shared IP, it's possible that another sender's poor practices are affecting your deliverability. Conversely, a decline in domain reputation usually stems from your own sending habits, such as high spam complaints, low engagement, or issues with your email content.

For specific insights into how major mailbox providers view your email, tools like Google Postmaster Tools are invaluable for Gmail performance. It provides data on IP reputation, domain reputation, spam rate, and delivery errors. If you're seeing little to no data, it often means the DNS record authentication may be misconfigured. However, remember that

Google Postmaster Tools only covers emails sent to @gmail.com accounts, not necessarily

Google Workspace or

Google for Education accounts.

Metric	Healthy range	Potential issue
Open rate	Varies by industry, but typically >15-20%	Emails landing in spam or being blocked. Also consider seasonality, as open rates for certain industries like HubSpot's edtech client will fluctuate widely.
Hard bounce rate	<1%	Outdated or invalid email addresses, indicating poor list hygiene.
Unsubscribe rate	<0.5%	Irrelevant content, excessive sending, or poor audience targeting.
Spam complaint rate	<0.1%	Recipients finding your emails unsolicited or low quality. Note that ESP-reported 0% might be inaccurate if you're sending to YahooGmailOutlook accounts.

Verifying email authentication and sender reputation

Email authentication is the bedrock of good deliverability. Without proper SPF, DKIM, and DMARC records, mailbox providers like

Gmail

Outlook

and Yahoo have no way to verify that your emails are legitimate, which can lead to them being routed to the spam folder or rejected outright. A sudden change in these records, even a minor one, can severely impact your sender reputation.

Your sender reputation is a score assigned to your sending IP address and domain based on your email sending history. Factors influencing this score include spam complaint rates, bounce rates, and engagement metrics like open and click-through rates. A low sender reputation is one of the primary reasons emails end up in spam. If you're on a shared IP (meaning you share an IP address with other senders), their poor reputation can negatively affect yours. While changing your sending domain or email address might seem like a quick fix, it's generally not recommended, as it can confuse recipients and further harm your reputation. Focus on addressing the root cause instead of trying to escape the issue.

Authentication best practices

Verify records: Ensure your SPF, DKIM, and DMARC records are correctly configured in your DNS.
Monitor DMARC reports: Analyze your DMARC reports to identify authentication failures.
Align domains: Ensure your From header domain aligns with your SPF and DKIM domains.

Content and list hygiene

The content of your emails plays a significant role in whether they land in the inbox or the spam folder. Spam filters constantly evolve, looking for patterns indicative of unsolicited mail. This includes overly promotional language, excessive use of all caps, suspicious links, and poor formatting. If your email engagement has dropped, it might be a sign that your content is no longer resonating with your audience or, worse, is triggering spam filters. A sudden and dramatic drop in open rates often signals deliverability issues.

List hygiene is another critical, yet often overlooked, factor. Sending emails to unengaged or invalid addresses can severely damage your sender reputation. High bounce rates indicate a stale list, while low engagement from active subscribers tells mailbox providers that your content isn't valuable, increasing the likelihood of future emails landing in spam. It's a continuous process to improve your email deliverability rates over time.

Common content issues

Spam trigger words: Words and phrases commonly associated with spam.
Poor formatting: Excessive images, too many fonts, or broken HTML.
Irrelevant links: Links to unverified or suspicious websites.

List hygiene best practices

Regular cleaning: Remove inactive or invalid subscribers.
Segment audiences: Send targeted content to engaged segments.
Double opt-in: Use a double opt-in process to confirm subscriber interest.

Advanced diagnostics and ongoing monitoring

While basic inbox placement tests can give you a snapshot, they often don't provide a complete or accurate picture of your deliverability to real subscribers. These tools might use static seed lists that don't fully replicate the dynamic filtering systems of major mailbox providers. This can lead to misleading results, making it seem like emails are going to spam when they might actually be delivered or vice versa.

For a comprehensive understanding, rely on DMARC aggregate reports. These reports offer a holistic view of your email traffic, showing authentication results (SPF, DKIM, DMARC), sending sources, and how mailbox providers are handling your mail, including rejections and quarantines. They are a much more reliable indicator of true deliverability issues than simulated tests. Another factor to check is whether your domain or IP has been placed on an email blocklist (sometimes called a blacklist). If you're on a blocklist, many emails will be rejected outright or sent directly to spam. You can use a blocklist checker to determine if your domain or IP is listed on any common blocklists.

Example DMARC record (p=none)

v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com;

Finally, review your sending infrastructure and identify any recent changes. Did you migrate to a new ESP, change your sending domains, or alter your sending volume significantly? Any abrupt change can trigger spam filters and impact your sender reputation. A new domain or IP address typically needs a warm-up period to build trust with ISPs, starting with low volumes and gradually increasing them.

Bringing your email program back on track

Diagnosing a sudden drop in email open rates and an increase in emails landing in spam requires a systematic approach. Start with a thorough review of your metrics, confirm your email authentication is correctly set up, scrutinize your content and list hygiene, and leverage advanced tools like DMARC reports. By understanding the interplay of these factors, you can effectively identify the root causes of your deliverability issues and implement targeted solutions.

The key is continuous monitoring and adaptation. Email deliverability is not a one-time fix but an ongoing commitment to best practices that ensure your messages consistently reach the inbox. Staying proactive and responsive to changes in your metrics and the email ecosystem will help maintain a strong sender reputation and optimal email performance.

Views from the trenches

Best practices

Actively monitor your sender reputation and deliverability metrics, looking for anomalies.

Ensure SPF, DKIM, and DMARC are always correctly configured and monitored.

Segment your audience and send relevant content to improve engagement.

Implement a double opt-in process to ensure list quality and subscriber intent.

Common pitfalls

Ignoring low open rates and high spam complaints, hoping they will resolve themselves.

Assuming 0% spam reports from your ESP is accurate, especially for major providers.

Changing your sending domain or email address to escape deliverability problems.

Over-relying on simple inbox placement tests that might provide inaccurate data.

Expert tips

Focus on domain reputation over IP reputation, as domain plays a larger role.

If sending to academic institutions, be aware their spam filters can be unique.

Engagement is paramount; a sudden drop can indicate content or targeting issues.

Always consider seasonality when analyzing open rates for specific audiences.

Expert view

Expert from Email Geeks says that unless you are sending to Yahoo, Gmail, free Microsoft, and Comcast domains, your ESP's reported complaint rate is likely inaccurate. You should review your rates over time to identify when the decrease began.

2025-07-08 - Email Geeks

Expert view

Expert from Email Geeks says there is nothing in the delivery, hard bounce, or unsubscribe rates that indicates a concern about the health of your list, suggesting the issue might lie elsewhere.

2025-07-08 - Email Geeks