How to troubleshoot Gmail performance issues and spam filtering?
Matthew Whittaker
Co-founder & CTO, Suped
Published 9 Jun 2025
Updated 16 Aug 2025
6 min read
Dealing with Gmail performance issues and emails landing in the spam folder can be a frustrating experience for any sender. Gmail, with its sophisticated filtering algorithms, sets a high bar for email deliverability, often being more stringent than other providers.
Many factors can contribute to these problems, from technical misconfigurations to content quality and recipient engagement. Understanding where to look and what actions to take is crucial for maintaining a healthy email program and ensuring your messages reach the inbox.
This guide will walk you through common troubleshooting steps, provide insights into Gmail’s filtering process, and offer practical solutions to help improve your email performance and prevent legitimate messages from being marked as spam.
Decoding Gmail's filtering logic
Gmail employs advanced artificial intelligence and machine learning to analyze incoming mail, dynamically adjusting its filters based on billions of data points. This includes not only technical aspects like authentication but also user interactions, such as marking emails as 'not spam' or reporting them as spam.
A key factor in Gmail's decision-making process is your sender reputation. This reputation is calculated for both your sending IP addresses and your domain. A strong reputation means your emails are likely to be delivered to the inbox, while a poor one can lead to messages being filtered to the spam folder or even outright rejected.
To gain visibility into Gmail's assessment of your sending practices, use Google Postmaster Tools. This free service provides detailed dashboards on your domain's and IP's reputation, spam rate, feedback loops, and authentication errors. Monitoring these metrics regularly is essential, as changes in sender behavior can impact deliverability within days.
Reputation Level
Description
Impact on Deliverability
Bad
A history of sending enormously high spam volumes.
Mail will almost always be rejected or marked as spam.
Low
Known to send considerable spam regularly.
Mail from this sender will likely be marked as spam.
Medium/Fair
Known to send good mail, but has occasionally sent a low volume of spam.
Most email will have fair deliverability, except when there is a notable increase in spam levels.
High
Has a good track record of a very low spam rate, and complies with sender guidelines.
Mail will rarely be marked by the spam filter.
Identifying the root causes of performance issues
Several factors can cause your emails to land in spam folders or experience deliverability issues with Gmail. Common culprits include problems with email authentication, poor sender reputation, low engagement from recipients, and even the content of your messages.
Authentication failures are a significant red flag for Gmail. If your emails fail SPF, DKIM, or DMARC authentication, Gmail is highly likely to mark them as spam or reject them outright. This is especially true after the recent 2024 sender requirements from Gmail and Yahoo.
Beyond authentication, your sender reputation is paramount. High bounce rates, low open rates, frequent spam complaints, or hitting spam traps can quickly degrade your reputation. Additionally, the content of your emails, including suspicious links, generic subject lines, or image-heavy messages with minimal text, can also trigger spam filters. To learn more, read our article Why your emails are going to spam.
Common pitfalls
Ignoring DMARC reports: Failing to analyze DMARC reports means you miss critical insights into authentication failures.
Not monitoring sender reputation: A declining reputation on Google Postmaster Tools often indicates underlying issues.
Sending to unengaged lists: Low open rates and high complaint rates signal disinterest and negatively impact deliverability.
Buying or renting email lists: These lists often contain spam traps, leading to blocklisting and severe reputation damage.
Strategic troubleshooting and monitoring
When facing deliverability or performance issues, proactive monitoring and systematic troubleshooting are essential. The first step is always to check your metrics in Google Postmaster Tools, specifically the IP and Domain Reputation dashboards. A sudden drop in reputation (e.g., from High to Medium/Fair or lower) is a clear indicator of a problem. You should also review the spam rate and authentication charts for anomalies.
Segmenting your audience can provide valuable insights. By comparing engagement rates for your Gmail recipients versus other domains, you can identify if the issue is specific to Gmail. A significantly lower open rate or higher complaint rate for Gmail users often indicates spam folder placement. Implement seed testing to see where your emails are landing across various mailbox providers.
For slow delivery issues, beyond typical server performance checks, consider running network diagnostic tests like ping and traceroute to Google's mail servers. This can help identify network latency or routing problems between your sending infrastructure and Gmail. You can find more details on this process in the Google Workspace Admin Help documentation.
Implementing fixes and best practices
Once you have identified the issues, focus on remediation. Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned. Use a DMARC monitoring service to continually collect and analyze reports, which will alert you to authentication failures and potential spoofing attempts. Check your IP and domain are not on any major blocklists.
Beyond technical setup, content and engagement are crucial. Optimize your email content to be relevant and valuable to your subscribers. Avoid excessive images, suspicious phrasing, or links to questionable domains. Regularly clean your email list to remove inactive subscribers, hard bounces, and known spam traps. Engaging recipients with personalized content can also significantly improve your sender reputation.
For new sending IPs or domains, implement a proper IP warm-up strategy, gradually increasing your sending volume to build a positive reputation. Consider including the Feedback-ID header in your emails. While not always effective for low spam rates, it can provide valuable insights if a large percentage of your traffic is marked as spam by recipients. You can find more about the Feedback-ID header in Google's documentation.
Actively use Google Postmaster Tools to track IP and domain reputation daily, identifying trends early.
Segment email lists to analyze engagement by domain, especially for Gmail recipients, to pinpoint specific issues.
Regularly clean email lists, removing inactive subscribers and hard bounces, to maintain high deliverability.
Ensure all email authentication protocols are correctly set up and aligned.
Implement Feedback-ID header to gain insights into user spam complaints.
Common pitfalls
Over-relying on seed tests without combining them with Postmaster Tools data.
Ignoring low engagement rates, which signal potential spam folder placement.
Not implementing DMARC or having it configured incorrectly, leading to authentication failures.
Sending emails with inconsistent content or sudden volume spikes that trigger spam filters.
Failing to monitor blocklists, which can severely impact sender reputation.
Expert tips
Continuously analyze email performance across different email service providers to catch Gmail-specific issues.
Prioritize email list quality over quantity, as engaged subscribers boost sender reputation.
Understand that deliverability is an ongoing process, not a one-time fix.
Utilize internal and external monitoring tools for a comprehensive view of your email health.
Adjust sending patterns and content based on recipient feedback and engagement metrics.
Marketer view
Marketer from Email Geeks says they test each email daily to various Gmail seeds to monitor placement.
2022-08-11 - Email Geeks
Marketer view
Marketer from Email Geeks says they compare open rates by domain and use lower Gmail open rates as a sign of more spam foldering, which leads to discussions about engagement and list hygiene.
2022-08-11 - Email Geeks
Maintaining a healthy email program
Troubleshooting Gmail performance issues and spam filtering requires a multifaceted approach, combining technical diligence with strategic content and list management. It is a continuous process that demands consistent monitoring and adaptation.
By understanding Gmail's complex filtering mechanisms, proactively monitoring your sender reputation through Google Postmaster Tools, ensuring robust email authentication, and focusing on delivering valuable content to engaged recipients, you can significantly improve your email deliverability and avoid the spam folder. Remember, a healthy email program is built on trust and consistent positive engagement with your audience.
