Why am I seeing spam spikes in Google Postmaster Tools?
Matthew Whittaker
Co-founder & CTO, Suped
Published 3 Aug 2025
Updated 14 Aug 2025
14 min read
Summary
Seeing unexpected spam spikes in Google Postmaster Tools (GPT), especially on days with no active sending, can be perplexing for email marketers. This phenomenon often leads to questions about data accuracy and the true health of one's email program. It's important to understand that GPT data has a certain lag and can be influenced by various factors beyond immediate sending activity, including historical email engagement and how Google calculates spam rates based on delivered mail to active users, not just opens. These spikes, while alarming, may not always indicate a current deliverability crisis if other metrics remain stable. Understanding the underlying causes is key to maintaining a healthy sender reputation and optimizing your email deliverability efforts.
Key findings
Data lag: Google Postmaster Tools data often lags actual sending activity, meaning spikes observed today might relate to emails sent days or even weeks ago. This delay can obscure the direct link between sending behavior and reported spam rates.
Old email complaints: Subscribers can mark old emails as spam, which, on days with low or no new sending volume, can disproportionately inflate the spam rate percentage in GPT. This is particularly true if the total volume of emails delivered to active inboxes is very small. You can learn more about how Google Postmaster Tools calculates spam rates.
Low sending volume amplification: When very few emails are sent, even a handful of spam complaints can lead to a high percentage spike, creating an exaggerated impression of a spam problem. For example, if only 14 messages reach the inbox and one is marked as spam, it results in a 7.1% complaint rate.
Domain reputation hierarchy: Activity on subdomains (like a bounce domain) can impact the reputation of the parent domain. If unmonitored sending from other sources uses your parent domain, this can influence the spam rates shown in GPT, even if your main sending operations are clean.
DMARC reports correlation: While DMARC reports provide insight into unauthorized sending (spoofing), they may not directly show issues related to legitimate but problematic sending from other departments (e.g., sales) that are properly authenticated. Reviewing your DMARC monitoring can still help identify broader authentication issues.
Key considerations
Focus on trends, not spikes: Instead of fixating on isolated daily spikes, monitor your spam rates and other GPT metrics for long-term trends. Consistent increases over time are more indicative of a problem than sporadic single-day anomalies. Further guidance on how to manage your Google Postmaster Tools data can be found in our guide on understanding Google Postmaster Tools V2 spam rate dashboard.
Investigate all sending sources: If you see unexpected spikes, broaden your investigation beyond your main email service provider (ESP) to include any other platforms or teams (e.g., sales, marketing, transactional systems) that might be sending emails using your domain or subdomains.
Understand GPT calculation: Recognize that GPT calculates spam rate as a percentage of mail delivered to the inbox of active users, not total sends or opens. This denominator can be small, leading to high percentages from few complaints.
Review email program holistically: Evaluate your entire email program for list hygiene, content quality, and engagement practices. Proactive measures in these areas can prevent real deliverability issues, even if GPT shows occasional unusual spikes.
Confirm domain authentication: Ensure all domains and subdomains used for sending are properly authenticated with SPF, DKIM, and DMARC. This helps Google correctly attribute sending activity and reputation.
What email marketers say
Email marketers often express confusion and concern when Google Postmaster Tools (GPT) displays spam spikes on days with little to no sending activity. Many have reported similar experiences, particularly observing specific spike percentages like 7.1%, which can lead to a perceived drop in domain reputation. While these spikes can be alarming, many marketers advise against overreacting to isolated incidents, emphasizing that real-time deliverability and long-term trends are more critical indicators. The consensus points to potential issues like delayed complaints on old emails or the impact of low sending volumes magnifying minor complaints.
Key opinions
Common occurrence: Several marketers report experiencing identical spam spikes (e.g., 7.1%) on the same dates, even with no recent email sends from the affected domain, suggesting a possible algorithmic quirk within GPT or a shared external factor.
Delayed complaints: A common theory is that these spikes are caused by subscribers marking old emails as spam days or weeks after they were sent, especially if the user rarely logs into their email account. This aligns with Google's data lag in GPT, as highlighted in Customer.io's documentation.
Reputation impact concerns: Many marketers worry that these seemingly unnatural spikes, even without active sending, negatively impact their domain reputation in GPT and subsequently, their overall deliverability.
Focus on real deliverability: Despite GPT spikes, some marketers note that their actual inbox placement, open rates, and click-through rates (CTR) remain stable, suggesting the spikes might be less critical than they appear. This reinforces the idea of not overreacting to single data points, a sentiment discussed in our article on 100% abuse rate on days with no email sends.
Key considerations
Beyond the from header: Marketers should look beyond the From header. Spam complaints in GPT are associated with the domain found in the d= tag of the DKIM signature, which might be different from the From address.
Subdomain impact: Using a subdomain for sending (e.g., bounce.yourdomain.com) can still affect the reputation of the parent domain (yourdomain.com), so all associated domains should be monitored.
Unaccounted sending: Investigate whether other departments (like a sales team) or third-party services are sending emails using your domain without your knowledge, as their practices could be causing complaints. This is often an overlooked aspect, as discussed by SendLayer.
GPT data limitations: Google Postmaster Tools does not show all data and the exact algorithms are proprietary. This makes it challenging to pinpoint the precise reason for every fluctuation.
Proactive monitoring: Regular monitoring of overall email performance metrics (opens, clicks, bounces, unsubscribes) in conjunction with GPT data offers a more comprehensive view of deliverability health. Even if you see a limited or intermittent data on GPT, keep an eye on other metrics.
What email marketers say
Marketer view
Email marketer from Email Geeks reports the exact same issue: a huge spike in spam rate on a specific date (Jan 18), even though no emails were sent from that domain for three weeks. This also occurred on Jan 4 and Nov 13, leading to a drop in domain reputation from high to medium, which has persisted.
21 Jan 2021 - Email Geeks
Marketer view
Marketer from Email Geeks indicates that their domain reputation also dropped to medium despite no sending activity. They find it odd but acknowledge the information is helpful.
21 Jan 2021 - Email Geeks
What the experts say
Email deliverability experts highlight that small complaint spikes in Google Postmaster Tools (GPT), even without recent sends, are often a consequence of how spam rates are calculated at low volumes. They emphasize that Google's data can lag significantly, and historical email interactions can trigger these spikes. Experts advise against over-analyzing every single spike, instead recommending a focus on long-term trends and ensuring all sending sources associated with a domain are properly managed and authenticated. The primary concern should be consistent inbox placement and recipient engagement, rather than isolated anomalies in GPT.
Key opinions
Low volume calculation: Periods of very low or no email sending can lead to inflated complaint spikes because the number of complaints is divided by a very small denominator (the number of emails delivered to active inboxes). This can result in high percentages from minimal actual complaints.
Lagging indicator: Domain reputation in GPT is a trailing indicator. It can take up to three weeks for changes in actual sender reputation to be reflected in GPT data, meaning observed spikes might be due to past sending activity rather than current. This delay is a known factor, as discussed in our article why is Google Postmaster Tools data delayed or missing?
Spam complaints on old emails: Subscribers can complain about old emails, even those sent months or a year ago, particularly if they rarely log into certain email accounts. These delayed complaints can contribute to spikes on non-sending days.
Multiple sending sources: Experts frequently point out that problems often stem from emails sent outside of the primary ESP, such as those from sales teams doing cold outreach or other systems using the same domain. Google can link these related domains and attribute their reputation.
Dynamic algorithms: Google's algorithms are constantly changing and are not fully transparent. Spending excessive time trying to reverse-engineer their exact mechanisms for every minor spike is often unproductive, as the insights may quickly become outdated.
Key considerations
Look at the d= value: For Google Postmaster Tools, the d= (DKIM signing domain) is the key value Google uses for calculating complaint rates. Any mail signed with your domain in the d= tag will contribute to your domain's reputation.
Differentiate reputation types: Understand that your main domain's reputation might differ from a subdomain's reputation used by an ESP, but they are linked. Discrepancies may indicate sending activity not tracked by your primary ESP.
Review overall email program: If GPT shows vastly different complaint rates for emails with your domain from different sources (e.g., your ESP vs. other internal teams), it suggests that other mailings are significantly impacting your complaint rate and overall reputation. This is where a holistic view of your email deliverability issues becomes critical.
Prioritize long-term performance: Focus on whether your mail consistently reaches the inbox and if you are maintaining consistent levels of opens and clicks over time. These metrics are stronger indicators of deliverability health than isolated complaint spikes.
Proactive investigation: Conduct sleuthing by talking to various internal stakeholders and reviewing logs to identify all sources sending mail under your domain, especially if they are using less-than-stellar lead lists.
What the experts say
Expert view
Expert from Email Geeks suggests that periods of no or very little mail sending can still lead to complaint spikes depending on how Google Postmaster Tools calculates its arithmetic. For example, a small number of complaints against a negligible volume of active emails can appear as a large percentage.
21 Jan 2021 - Email Geeks
Expert view
Expert from Email Geeks explains that just because you haven't sent emails recently, it doesn't mean a subscriber isn't complaining about an old email. This behavior occurs more often than one might think.
21 Jan 2021 - Email Geeks
What the documentation says
Official documentation and industry research consistently highlight that Google Postmaster Tools (GPT) provides aggregate data, not real-time or granular insights. The spam rate displayed is often a reflection of messages authenticated by DKIM with your domain and delivered to active Gmail inboxes. It's a key indicator of recipient feedback, but its daily fluctuations, especially during low sending periods, are a known characteristic rather than necessarily a sign of immediate crisis. The underlying principle is that Google's systems are designed to identify patterns of abuse and adapt to protect users, so isolated spikes need to be considered in the broader context of long-term sending reputation.
Key findings
Spam rate definition: Google Postmaster Tools defines spam rate as the percentage of emails identified as spam by users and Google's filters, specifically for DKIM-authenticated messages sent to Gmail accounts. This percentage is not based on total sends, but on messages that land in the active inbox.
Data aggregation: GPT provides aggregate data for a given day or period, meaning it reflects cumulative performance. Sudden spikes can occur when the base volume of emails delivered to the inbox is very small, making a few complaints appear as a large percentage.
Threshold lines: As of 2025, Google Postmaster Tools includes threshold lines to help senders visualize whether their spam rate complies with or violates Google's guidelines, specifically highlighting the 0.3% threshold for avoiding deliverability issues.
Feedback loops (FBLs): GPT provides a feedback loop identifier that allows senders to identify specific campaigns or streams of email messages that generate spam complaints. Ignoring these alerts can lead to consistent spam folder placement.
Reputation categories: Google rates domain and IP reputation as Bad, Low, Medium, or High. A Bad reputation indicates a history of high spam complaints, leading to lower deliverability.
Key considerations
Data delay: Be aware that GPT data is not real-time and can be delayed by a few days. Therefore, a spike seen today might reflect sending activity from days prior, or even complaints on very old emails, rather than immediate issues.
Minimum volume for data: If you send low volumes of emails, GPT may show no data or highly fluctuating numbers because there isn't enough traffic to provide stable metrics.
Holistic view: Use GPT in conjunction with other internal email analytics (e.g., ESP reports, open rates, click rates, bounce rates) to get a comprehensive picture of your email program's health, as GPT alone may not provide all the answers. Additional data points can help you resolve deliverability issues, as suggested by Kickbox Blog.
Proactive hygiene: Implement strict list hygiene practices, including removing unengaged subscribers and monitoring for spam traps, to minimize the likelihood of receiving spam complaints regardless of sending volume.
Authentication importance: Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned for all sending domains. Google relies heavily on these authentications to determine sender reputation and filter incoming mail. Our guide on DMARC, SPF, and DKIM provides a good starting point.
Technical article
Google documentation highlights that Postmaster Tools data, including spam rates, can be a few days behind real-time sending. This lag means that a spam spike observed today might originate from emails sent on a previous day, making it crucial to consider the delay when interpreting the data.
22 Mar 2025 - Customer.io
Technical article
The Iterable blog states that as of 2025, Google Postmaster Tools added threshold lines to help senders easily visualize whether their spam rate complies with or violates established guidelines, providing clearer indicators for reputation management.
