Summary
Diagnosing email throttling, particularly with Gmail, can be a complex task, even when your IP and domain reputations appear to be in good standing. Google Postmaster Tools (GPT) provides invaluable data that can help unravel these issues, offering insights beyond simple reputation scores. While an email service provider (ESP) might suspect throttling based on slow delivery, GPT can offer concrete data points to confirm or refute such hypotheses, especially regarding specific IP addresses.
Key findings
- Throttling possibility: Even with a spotless IP or domain reputation, throttling can still occur.
- Per-IP reputation: Google assesses and provides reputation data for each individual IP address, not just an aggregate score.
- Detailed visibility: GPT allows you to inspect the specific IPs from which Google received mail on any given day, offering granular insights into traffic. Mailgun provides further details on sender reputation.
- Transient failures: Email throttling often manifests as temporary (transient) bounce errors, which may not always appear in standard bounce logs if the ESP retries delivery.
- Delivery delays: Unusual or significant delays in email delivery to Gmail recipients are a strong indicator of throttling, even without explicit bounce codes.
Key considerations
- Validate IP data: Use GPT to click on specific days and review the IPs that Google registered mail from for your domain.
- Request detailed logs: Ask your ESP for comprehensive delivery logs, including transient failures and the number of delivery attempts for delayed emails. Without this, it's hard to interpret missing data.
- Understand ESP behavior: Be aware that ESPs often employ back-off measures, temporarily pausing delivery to circumvent rate limitations, which might mask throttling in basic reports.
- Monitor deliverability metrics: Regularly review key email deliverability metrics in GPT to identify any unusual trends or declines in performance. For example, Iterable details various data points.
What email marketers say
Email marketers often find themselves in a challenging position when their emails experience delays or non-delivery without clear indications like hard bounces or blacklistings. Many rely on their ESP's reporting, but this can sometimes lack the granular detail needed to diagnose subtle issues like throttling. The general consensus among marketers is a need for more transparent and actionable data to confirm suspicions of throttling, especially when general reputation metrics appear fine.
Key opinions
- Reputation vs. throttling: Marketers frequently note that even with excellent IP and domain reputations, throttling by providers like Google can still occur.
- Expectation of bounce codes: Many marketers anticipate seeing 4.x.x or 5.x.x bounce codes in their logs as evidence of throttling or delivery issues.
- Inconsistent IP performance: Observing that one IP delivers normally while another experiences slowdowns during the same period is a strong indication of a problem on the throttled IP.
- ESP 'hunches': ESPs might offer hypotheses about throttling without providing concrete data, leading to uncertainty.
Key considerations
- Deep dive into logs: Don't just rely on summary reports; insist on detailed delivery logs from your ESP to uncover transient failures and delivery attempts. You can also monitor your domain reputation.
- Correlate with GPT: Cross-reference observed slow delivery times with GPT's IP reputation dashboard to see if a particular IP is experiencing issues. SendLayer explains how to monitor email deliverability.
- Understand ESP retry logic: Knowing how your ESP handles temporary errors and retries can explain why throttling isn't immediately visible as a bounce.
- Focus beyond reputation: Recognize that even good reputation scores don't guarantee unrestricted delivery; other factors can lead to spam placement or throttling.
Marketer view
Email marketer from Email Geeks indicates that throttling can occur even when both IP and domain reputations are spotless, suggesting that a positive reputation alone does not guarantee unimpeded delivery.
Marketer view
Marketer from a Reddit user points out that observing large volumes of 4.x.x (transient) and 5.x.x (permanent) bounce codes in logs is expected if throttling is genuinely happening, especially during periods of slow delivery.
What the experts say
Experts in email deliverability emphasize that Google Postmaster Tools is a critical, though sometimes misunderstood, resource for diagnosing sophisticated issues like throttling. They clarify that Google provides granular data at the IP level, and that transient failures, often indicative of throttling, may not be explicitly logged as bounces by ESPs. This calls for a deeper look into delivery logs and an understanding of how ESPs manage their retry mechanisms.
Key opinions
- IP-level reputation: Experts confirm that Google assigns reputation on a per-IP address basis, not as a single aggregate score for a domain.
- Direct IP validation in GPT: It is possible to click on a specific day within GPT to see the individual IPs from which Google observed mail for your domain. This can help fix issues with GPT not working.
- Transient bounce obscurity: Depending on the ESP, detailed information on transient failures (temporary bounces due to rate limitations) might not be readily available in standard bounce logs.
- ESP back-off measures: Many ESPs implement back-off strategies, temporarily pausing delivery after specific transient failures to circumvent limitations. DuoCircle discusses monitoring IP performance.
- Delayed delivery insights: If an ESP retries delivery, slow delivery might be the only visible symptom, rather than explicit bounces.
Key considerations
- Granular data review: Actively use the drill-down feature in GPT to scrutinize per-IP reputation and identify any specific IPs experiencing issues.
- Detailed log requests: It's crucial to request detailed delivery logs from your ESP, including transient failure records and delivery attempt counts, to properly diagnose throttling.
- ESP communication: Engage with your ESP to understand their specific handling of transient failures and back-off measures to interpret their reports accurately.
- Cross-reference data: Compare GPT data with your internal send logs and ESP reports to build a comprehensive picture of deliverability performance and identify potential throttling.
Expert view
Expert from Email Geeks clarifies that Google provides reputation data per individual IP address, indicating that there is no aggregate reputation score provided by GPT.
Expert view
An expert from SpamResource.com suggests that email throttling often results in temporary errors (4xx codes) which, if retried by the sending system, may not appear as bounces but rather as significant delivery delays to recipients.
What the documentation says
Google's official documentation for Postmaster Tools outlines the various dashboards and metrics available to senders. It emphasizes the importance of monitoring IP and domain reputation, spam rates, and delivery errors to maintain good standing with Gmail. While it doesn't explicitly detail how to diagnose throttling, it provides the fundamental data points and tools necessary to infer such issues from trends in reputation, delivery rates, and error patterns.
Key findings
- Reputation dashboards: GPT offers dedicated dashboards for IP reputation and domain reputation, categorizing them as bad, low, medium, or high.
- Delivery errors chart: This chart shows the percentage of your total traffic that was rejected or temporarily failed due to various reasons, which can include throttling due to unusual sending patterns.
- Spam rate monitoring: The spam rate dashboard shows the volume of user-reported spam over time, a key factor impacting deliverability and potential throttling. Learn more about the GPT V2 spam rate dashboard.
- Authentication charts: Charts for SPF, DKIM, and DMARC indicate the percentage of your mail that passes these authentication checks, which are fundamental to trust and avoiding throttling.
Key considerations
- Trend analysis: Regularly review the historical data in GPT to identify any sudden dips in reputation or spikes in delivery errors corresponding to suspected throttling.
- Volume thresholds: Be aware of Google's volume thresholds for bulk senders and new sender requirements, as failure to comply can lead to throttling. This is a key part of Google Postmaster compliance.
- Feedback loops: Utilize feedback loops (FBLs) available through GPT to understand user complaints, as high spam complaints directly impact reputation and can trigger throttling.
- DMARC reports: Analyze DMARC reports (specifically aggregate reports) to gain a holistic view of your sending ecosystem and any authentication failures that might contribute to throttling. MailMonitor explains optimizing marketing efforts.
Technical article
Documentation from Google Postmaster Tools Help outlines that senders can view a Delivery Errors chart, which displays the percentage of their mail that was rejected or temporarily failed due to various reasons, offering clues about throttling.
Technical article
Documentation from Gmail Help states that senders should aim to maintain high IP and domain reputation, as these are primary factors influencing delivery and can lead to throttling if they decline.
Related resources
10 resources
Related pages
How effective is Google Postmaster Tools for tracking email spam placement during IP warming?
What are the current issues and status of Google Postmaster Tools?
What email deliverability metrics to monitor in Google Postmaster Tools?
Troubleshooting dips in DKIM success rate in Google Postmaster Tools
What is Google's Postmaster API and what insights does it provide?
How to interpret and identify spam complaints using Google Postmaster Tools?
How to troubleshoot SPF failures in Google Postmaster Tools and improve email delivery?
Ultimate Guide to Google Postmaster Tools V2
How to Improve Domain Reputation Using Google Postmaster Tools [2025 Guide]
Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
