What steps should I take to troubleshoot a sudden drop in email delivery rates?
Michael Ko
Co-founder & CEO, Suped
Published 2 May 2025
Updated 17 Aug 2025
5 min read
A sudden drop in email delivery rates can be alarming. It means your messages aren't reaching intended inboxes, directly impacting your communication and business objectives. Understanding the root cause is crucial for a swift recovery.
The challenge often lies in pinpointing the exact issue, as many factors influence email deliverability. I will walk through the critical steps to diagnose and resolve a sharp decline in your email delivery.
Initial diagnosis and data collection
When I see a sudden drop, the first thing I do is gather as much data as possible. Your email service provider (ESP) dashboard is the primary source for this. Look for reports detailing bounces, deferrals, and spam complaints.
Pay close attention to the specific domains affected. Is the drop widespread across all recipients, or concentrated on particular providers like Gmail or Yahoo? This can significantly narrow down your investigation. If it's a specific domain like Yahoo, it often points to particular issues that need targeted approaches. You might find it useful to understand more about how to troubleshoot issues with a dropping Yahoo email delivery rate.
If your ESP provides them, examine the full text of bounce messages. These messages contain error codes and descriptions that directly tell you why emails are being rejected. Without this information, troubleshooting becomes a guessing game.
Technical foundations and authentication
A common culprit behind deliverability drops is issues with email authentication. Ensuring your domain's SPF, DKIM, and DMARC records are correctly set up and aligned is fundamental. These records prove to receiving servers that you are a legitimate sender.
A sudden change in your delivery rate might indicate a recent change to your DNS records or sending infrastructure. Even minor misconfigurations can lead to significant delivery problems. For instance, an SPF TempError can lead to issues with delivery. You can learn more about demystifying the SPF TempError.
You can use a DMARC record generator tool to ensure your DMARC records are properly formatted and published. This is an essential step for robust email security and deliverability.
Checking your DNS records
SPF: Verify your SPF record includes all authorized sending IPs and domains. An incorrect SPF record can lead to emails being marked as spam or rejected.
DKIM: Ensure your DKIM signatures are valid and your public key is correctly published in your DNS. A DKIM body hash mismatch is a common cause of authentication failures.
DMARC: Confirm your DMARC policy is correctly implemented and that you're receiving DMARC reports. These reports provide invaluable insight into your email authentication status and potential delivery issues. You can use a DMARC monitoring tool to help collect and analyze these reports.
Sender reputation and list health
Your sender reputation is paramount. A sudden drop often correlates with a decline in how mailbox providers perceive your sending practices. Factors like high spam complaint rates, a surge in bounce rates, or hitting spam traps can severely damage your reputation. Understanding why email deliverability rates are dropping can help.
Regularly cleaning your email list is a critical proactive measure. Removing inactive or invalid email addresses can prevent hard bounces and reduce the likelihood of hitting spam traps, both of which negatively impact your sender score.
Monitor your blocklist (or blacklist) status. Getting listed on a major blocklist can immediately halt your email delivery to affected mailboxes. Understanding what happens when your domain is on an email blacklist is key to responding effectively.
Common deliverability problems
High bounce rates: Sending to invalid or outdated email addresses.
Increased spam complaints: Recipients marking your emails as spam due to irrelevance or unwanted content.
Blocklist inclusion: Your IP or domain getting listed on a blocklist (blacklist) due to suspicious activity or poor sending practices.
Low engagement: Recipients consistently not opening or clicking your emails, signaling low interest.
Effective solutions
List cleaning: Regularly remove unengaged and invalid contacts to maintain a healthy list.
Content optimization: Improve email relevance, personalization, and value to reduce complaints and increase engagement.
Blocklist monitoring: Actively monitor major blocklists (blacklists). If listed, follow delisting procedures immediately, or use a blocklist checker.
Audience segmentation: Send targeted content to engaged segments to improve overall engagement metrics.
Content and sending practices
Even with perfect technical setup, content quality and sending patterns can trigger delivery issues. A sudden change in content, such as new links, images, or keywords, might inadvertently trigger spam filters. Also, abrupt spikes in sending volume without proper IP warming can be red flags. Consider diagnosing an unexpected drop in engagement.
Review any recent changes to your email templates, subject lines, or sending frequency. Sometimes, minor tweaks can have unintended consequences on how your emails are perceived by recipient servers. Ensure your content remains relevant and provides value to your subscribers. You might also find it helpful to troubleshoot email open rate drops.
Pay attention to engagement metrics beyond just delivery. A sudden drop in open rates or click-through rates (CTR) often precedes a delivery rate decline, as low engagement signals to ISPs that your emails are not desired. Diagnosing and improving email deliverability and open rates should be an ongoing effort.
Proactively monitor deliverability metrics including bounce rates, deferrals, and spam complaints.
Segment your audience and tailor content to maintain high engagement levels.
Regularly clean your email list to remove invalid and unengaged recipients.
Common pitfalls
Ignoring bounce messages or not having access to detailed bounce data from your ESP.
Making sudden changes to sending volume or content without proper testing or warming.
Neglecting sender reputation monitoring, leading to undetected blocklist inclusions.
Expert tips
Always obtain full bounce messages from your ESP; they provide the clearest indication of delivery issues.
Prioritize addressing issues with specific large mailbox providers, as they can disproportionately affect overall delivery rates.
Before escalating, confirm that your issue is a widespread delivery rate drop and not just an anomaly from a single campaign.
Expert view
Expert from Email Geeks says that when diagnosing a drop in email delivery rates, first determine if the issue is a sudden spike in bounces or deferrals.
Oct 22, 2024 - Email Geeks
Expert view
Expert from Email Geeks says it is important to understand which recipient domains are affected. If rejections are limited to specific providers like
Oct 22, 2024 - Email Geeks
Maintaining healthy email deliverability
Troubleshooting a sudden drop in email delivery rates requires a systematic approach, starting with data collection and moving through technical checks, reputation management, and content review. Proactive monitoring and adherence to best practices are key to preventing such issues. You can also utilize an email deliverability tester.
While initial drops can be alarming, most deliverability issues are solvable with diligent investigation and corrective action. By focusing on the health of your sending infrastructure and the quality of your recipient list, you can maintain strong email performance.
Gmail or 
Yahoo? This can significantly narrow down your investigation. If it's a specific domain like Yahoo, it often points to particular issues that need targeted approaches. You might find it useful to understand more about how to troubleshoot issues with a dropping Yahoo email delivery rate.
