Why is my DMARC success rate suddenly dropping, and how does this affect spam rates and blocklists?
Matthew Whittaker
Co-founder & CTO, Suped
Published 12 Jul 2025
Updated 15 Aug 2025
9 min read
A sudden drop in your DMARC success rate can be a truly alarming indicator. It often appears to coincide with other issues, like a spike in spam complaints or finding your domain or IP address listed on various blocklists (or blacklists). It's easy to feel overwhelmed, wondering what's causing what and where to even begin addressing the problem.
When the DMARC success rate suddenly plummets from 100% to a much lower figure, it signals that emails purporting to be from your domain are failing authentication checks. This can be due to legitimate mail streams that are not correctly set up, or it could indicate that unauthorized parties are spoofing your domain for malicious purposes. The key to understanding this drop, and its potential ripple effects, lies in diligently examining your DMARC reports.
It's a common scenario to see these issues surface simultaneously. My goal here is to help you decipher what's happening, understand the relationships between DMARC failures, spam rates, and blocklistings, and provide a clear path forward for troubleshooting and resolution. By understanding the underlying causes, you can implement effective strategies to restore your email deliverability and protect your sender reputation.
The most common reason for a sudden drop in DMARC success rate is the sending of emails from your domain that are not properly authenticated by SPF or DKIM, or fail DMARC alignment. This can happen if new sending platforms are introduced without proper configuration, or if existing configurations are inadvertently changed. It's also a strong signal that someone might be forging your domain to send spam.
DMARC reports provide granular insight into these failures. These reports, sent by receiving mail servers to the email address specified in your DMARC record, detail which messages passed and failed DMARC authentication, the sending IP addresses involved, and the authentication results for SPF and DKIM. Without these reports, you are essentially flying blind, unable to pinpoint the exact source of the problem.
Sometimes, teams within your organization, such as a sales team, might begin using a new email service provider (ESP) or a cold outreach tool that hasn't been correctly configured for DMARC. This unauthenticated mail, though legitimate in its intent, will fail DMARC checks, leading to a drop in your overall success rate and potentially impacting your domain reputation. It's crucial to ensure all sending sources are authenticated.
Investigating DMARC failures
When your DMARC success rate drops, it's a clear signal to dive into the data. DMARC reports specify the IP addresses and authentication results (SPF, DKIM) for all emails purporting to be from your domain.
Identify unauthorized senders: Look for IPs or domains that are sending mail on your behalf without proper authentication.
Review legitimate services: Check if any of your known third-party ESPs or marketing automation platforms are failing authentication.
Examine authentication status: Verify if SPF or DKIM failures are causing the DMARC drop, as DMARC relies on these.
DMARC and spam rates
While a DMARC success rate drop indicates authentication issues, it doesn't directly translate into a higher user-reported spam rate. Most end-users are unaware of DMARC and how it works. They classify emails as spam based on content, relevance, and their own inbox experience.
However, there's an indirect connection. If the DMARC drop is due to spammers forging your domain, and they are sending high volumes of unsolicited mail, this will likely lead to a surge in spam complaints. Even if your legitimate mail is separate, the overall reputation of your domain can be negatively affected due to the increased volume of spam associated with it. Mailbox providers like Google and Yahoo monitor spam rates closely, and a high rate can lead to your emails being filtered or blocked.
Conversely, if the DMARC drop is because your own legitimate email is suddenly failing authentication, those emails might start landing in spam folders or being rejected. This will naturally lead to a drop in engagement metrics like open and click-through rates. While recipients might not explicitly mark these as spam, the overall deliverability of your legitimate emails will suffer, contributing to a perceived rise in spam. You can learn more about why your emails go to spam in this guide.
DMARC failures and blocklists
Most public blocklists (sometimes called blacklists) do not directly consider DMARC authentication failures when listing an IP address or domain. Blocklists typically list entities based on spam complaints, spam trap hits, sending to invalid addresses, or exhibiting other abusive sending behaviors. So, a DMARC mismatch alone won't get you listed on a common blocklist like Spamhaus, though some private blocklists used by larger mailbox providers might factor it in.
However, similar to spam rates, there's an indirect path to blocklisting. If your DMARC success rate drops because spammers are actively forging your domain and sending large volumes of malicious or unwanted email, those activities can lead to the IP addresses they use (or even your domain, in severe cases) being added to blocklists. Even if this isn't your sending, your brand's reputation can suffer. If the blocklist listing is on a shared IP address, the actions of other senders on that IP can also affect you, regardless of your DMARC status. This is explained further in our in-depth guide to email blocklists.
Therefore, while DMARC failure itself isn't a direct cause for blocklisting, it often points to underlying issues that *can* lead to blocklistings. For example, a high volume of DMARC-failing emails could be an indication of spam operations using your domain, which in turn could result in your domain being blacklisted (or blocklisted) by various reputation services.
Policy impact: Depending on your DMARC policy (p=none, quarantine, reject), failing emails may still deliver or be affected.
Direct impact on deliverability: Failing emails are more likely to land in spam, but this is a deliverability filter, not a blocklist action.
Blocklist (or blacklist) listing
Reputation issue: Triggered by high spam complaints, spam traps, or invalid addresses.
Wider consequences: Can lead to widespread email rejection by receiving mail servers.
Indirect DMARC link: While DMARC doesn't cause listing, unauthenticated spam from your domain might.
Troubleshooting a simultaneous drop
When facing a simultaneous drop in DMARC success rates, a spike in spam complaints, and blocklisting, it's essential to approach the problem systematically. Your DMARC reports are the first place to look. They offer the most direct evidence of what's happening with your domain's email authentication. If you're on a shared IP address, remember that the actions of other senders on that IP can affect your deliverability, leading to blocklist listings that aren't directly related to your sending practices or DMARC.
After reviewing your DMARC reports, if you identify legitimate sending sources that are failing DMARC, prioritize correcting their SPF and DKIM configurations. Ensure that all email service providers, marketing platforms, and internal systems sending on your behalf are properly authenticated and aligned with your DMARC policy. This might require coordination with your IT or engineering team, as DNS record access is often necessary.
If DMARC reports show significant volumes of unauthenticated mail from unknown IPs, it's likely domain spoofing. In this case, moving your DMARC policy to a stronger enforcement level (like p=quarantine or p=reject) can help mitigate the impact of these fraudulent emails on recipients and protect your brand, but only after all your legitimate email streams are authenticated. You can use a DMARC record generator to assist with this process.
Finally, address the spam rate and blocklisting issues. If the spam complaints are coming from your legitimate mail, review your content, list hygiene, and sending practices. High complaint rates or engagement with inactive lists can damage sender reputation. For blocklistings, identify the specific blocklist and the reason for the listing, then follow their delisting procedures. This holistic approach ensures you tackle all symptoms and underlying causes.
Views from the trenches
Best practices
Always monitor your DMARC reports. They are the single source of truth for email authentication.
Ensure all legitimate sending services are properly configured with SPF, DKIM, and DMARC alignment.
Segment your email lists and warm up new IPs gradually to avoid sudden spikes in sending volume.
Common pitfalls
Ignoring DMARC reports or not having a system to process them can leave you blind to spoofing.
Assuming DMARC failures directly lead to blocklisting. It's usually indirect through spam activity.
Not coordinating with all teams (e.g., sales, marketing, IT) on new sending platforms.
Expert tips
If on shared IPs, your DMARC success rate might fluctuate due to other senders, not just your own.
Gmail complaints are domain-based, not IP-based, so a shared IP blocklist might not explain your spam spike.
A drop in DMARC success is often due to unauthenticated mail from your domain, either legitimate or forged.
Expert view
Expert from Email Geeks says that a DMARC drop indicates unauthenticated mail from your domain, which could be legitimate but misconfigured, or a result of someone forging your domain.
2020-12-01 - Email Geeks
Expert view
Expert from Email Geeks says that DMARC reports are essential for identifying exactly what email is failing, including the sending IP and SPF/DKIM status.
2020-12-01 - Email Geeks
Restoring your email deliverability
A sudden drop in your DMARC success rate, coupled with increased spam complaints and blocklist issues, can be daunting. The key is to understand that while these issues often appear together, their direct causal links vary. DMARC primarily addresses email authentication and domain spoofing. Spam rates are influenced by recipient engagement, content quality, and legitimate sending practices. Blocklists typically react to sending behaviors associated with unsolicited or problematic mail, such as high bounce rates or spam complaints.
The most effective way to diagnose and resolve these intertwined problems is to start with your DMARC reports. These reports will tell you whether the failing emails are from your known sending infrastructure or from unknown, potentially malicious, sources. Once you identify the source of the DMARC failures, you can take appropriate action, whether that's reconfiguring legitimate senders or moving to a stricter DMARC policy to protect against spoofing.
By proactively monitoring your DMARC reports, maintaining proper authentication for all email streams, and consistently practicing good email hygiene, you can significantly improve your overall deliverability and maintain a strong sender reputation. This comprehensive approach ensures your emails reach their intended inboxes, free from the shadow of spam folders or blocklist (blacklist) entanglements.
Google and Yahoo monitor spam rates closely, and a high rate can lead to your emails being filtered or blocked.
Spamhaus, though some private blocklists used by larger mailbox providers might factor it in.
