Summary
Google employs sophisticated email filtering algorithms considering complaint rates, engagement, sender reputation, and content quality to determine inbox placement. While Google aims to isolate different email streams from the same domain, high complaint rates across any stream can negatively impact overall deliverability. Maintaining a spam rate below 0.10% is crucial. Email deliverability depends on actively monitoring complaint rates via tools like Google Postmaster Tools, improving subscriber engagement, implementing feedback loops, using proper email authentication, and segmenting email streams to mitigate deliverability risks. Sender reputation, especially IP reputation, significantly influences deliverability, highlighting the importance of careful sending practices and responsible list management. Basic deliverability rules must be adhered to, which include enabling one-click unsubscription.
Key findings
- Holistic Approach: Google utilizes a comprehensive algorithm encompassing numerous factors for email filtering.
- Impact of Complaints: A high rate of user-reported spam is a critical factor impacting deliverability and sender reputation.
- Google Isolation Attempts: Google attempts to isolate email streams but does not always succeed which means that any issue in one stream can affect other streams.
- Actionable Metrics: Sender Score, SNDS and Google Postmaster Tools provide actionable metrics for monitoring and improving deliverability.
- Critical Basics: Core deliverability is ensured by proper authentication, engagement and easy unsubscription which includes one-click capabilities.
- Importance of IP: IP reputation remains a key indicator of your overall sending reputation.
Key considerations
- Monitor Metrics: Consistently monitor Google Postmaster Tools, Sender Score, and SNDS.
- Reduce Spam Rates: Implement practices to reduce the number of users marking emails as spam.
- Improve Engagement: Focus on delivering valuable content that encourages recipient interaction.
- Authentication: Ensure SPF, DKIM, and DMARC are properly configured.
- Feedback Loops: Set up feedback loops to receive and address complaint data from ISPs.
- Check IP Reputation: Always check IP reputation to avoid any impact on reputation.
- One Click Unsubscription: Enable one-click unsubscription to encourage easier unsubscribing.
What email marketers say
12 marketer opinions
Google's email filtering system uses complex algorithms, including complaint rates, engagement metrics, sender reputation, and content quality to determine inbox placement. High complaint rates negatively impact sender reputation and can lead to emails being delivered to the spam folder or blocked entirely. Google is also adept at fingerprinting and separating different email streams from the same domain, meaning issues in one stream can affect others. Maintaining a good sender reputation, monitoring complaint rates, and focusing on subscriber engagement are crucial for ensuring email deliverability.
Key opinions
- Complaint Rate Impact: High complaint rates directly influence spam filtering decisions by ISPs, leading to potential blocking or spam folder placement.
- Google's Algorithms: Google uses complex algorithms that consider complaint rates, engagement metrics, sender reputation, and content quality to filter emails.
- Sender Reputation: Maintaining a good sender reputation is crucial for avoiding the spam folder; this is influenced by complaint rates, bounce rates, and engagement.
- Stream Separation: Google is capable of distinguishing different email streams from the same domain, impacting deliverability differently.
- Engagement Matters: Subscriber engagement metrics (open rates, click-through rates) alongside complaint rates influence inbox placement.
Key considerations
- Monitor Complaint Rates: Regularly monitor complaint rates in tools like Google Postmaster Tools to identify and address deliverability issues promptly.
- Improve Engagement: Focus on improving subscriber engagement through relevant content and clear calls-to-action to reduce the likelihood of spam complaints.
- Authenticate Emails: Ensure proper email authentication (SPF, DKIM, DMARC) to improve sender reputation and signal legitimacy to ISPs.
- Segment Sending: Segment email streams to isolate and address deliverability issues within specific campaigns or types of emails.
- Utilize Feedback Loops: Implement feedback loops (FBLs) to receive complaint data directly from ISPs and address issues promptly.
Marketer view
Marketer from Email Geeks agrees with Laura, stating that Google is good at fingerprinting certain types of sends, even from the same domain, and diluting is a dangerous game.
5 Jul 2021 - Email Geeks
Marketer view
Marketer from Email Geeks shares experience of having clients sending shopping cart abandonment emails and newsletters from the same IP/domains, where the newsletters got 100% Gmail inbox placement, and the SCAEs got bulked.
8 Jun 2024 - Email Geeks
What the experts say
4 expert opinions
Google's email filtering is sophisticated, often separating different email streams from the same sources. While high complaint rates are a concern, the impact may vary depending on the specific stream. Google employs machine learning to detect patterns and trends, making reputation impact assessment complex. Sender reputation, particularly IP reputation, significantly influences deliverability; using shared IPs links your reputation to others' practices. Essential deliverability practices include authentication, sending desired mail, and easy unsubscription options.
Key opinions
- Stream Separation: Google can differentiate email streams, mitigating the broad impact of isolated high complaint rates.
- Machine Learning: Google uses machine learning to assess patterns and trends, making it challenging to predict precise reputation impacts.
- IP Reputation Lag: IP reputation is a lagging indicator affecting deliverability, especially with shared IPs.
- Fundamentals Matter: Email deliverability relies on authentication, sending desired content, and easy unsubscription options.
Key considerations
- Monitor Streams: Continuously monitor the complaint rates of each individual stream and address any critical deliverability issues.
- Audit Sending Practices: Review and audit your sending practices for each mail stream for sending unwanted mail to recipients or outdated contact data.
- Address Source: Using dedicated IPs may give you more reputation control.
- Ensure Best Practices: Adhere to fundamental deliverability practices, especially authentication and easy unsubscription.
Expert view
Expert from Spam Resource explains that IP reputation is a lagging indicator of your sending practices and can have a significant impact on deliverability. They also highlight that using shared IP addresses means your reputation is linked to the behaviour of all users sending from that IP.
7 Jul 2023 - Spam Resource
Expert view
Expert from Email Geeks shares that Google is very good at separating out different email streams, even from the same IPs and with the same identifiers, so a big campaign shouldn't necessarily be impacted by the high complaint rate of smaller, automated sends.
8 Apr 2025 - Email Geeks
What the documentation says
4 technical articles
Google recommends maintaining a spam rate below 0.10%, not exceeding 0.30%, to avoid spam filtering. High spam rates, as reported in Google Postmaster Tools, directly correlate with users marking emails as spam, damaging sender reputation and inbox placement. Feedback Loops (FBLs) provide complaint data, enabling senders to address root causes. Microsoft's SNDS offers data on complaint rates and spam trap hits, aiding in resolving deliverability issues specifically within Microsoft's ecosystem.
Key findings
- Spam Rate Thresholds: Google advises keeping spam rates below 0.10% and never above 0.30%.
- Direct Correlation: High spam rates directly indicate users are marking emails as spam.
- Feedback Loops (FBLs): FBLs are crucial for receiving and acting on complaint data from ISPs.
- SNDS Importance: Microsoft SNDS aids in addressing deliverability specifically for Microsoft email services.
Key considerations
- Monitor Spam Rate: Consistently monitor spam rates in Google Postmaster Tools.
- Investigate High Rates: Thoroughly investigate and address the root causes of high spam rates.
- Implement FBLs: Implement and actively use FBLs to identify and resolve complaint issues.
- Utilize SNDS Data: Leverage SNDS data to identify and address deliverability concerns specific to Microsoft email users.
Technical article
Documentation from SparkPost explains that feedback loops (FBLs) are a mechanism where ISPs forward complaint data back to the sender. Monitoring and acting on FBL data is critical for identifying and addressing the root causes of complaints.
16 Sep 2022 - SparkPost
Technical article
Documentation from Google Postmaster Tools highlights that a high spam rate indicates that users are marking your emails as spam. Aim to keep this rate low to maintain a good sender reputation and ensure emails reach the inbox.
24 Nov 2023 - Google Postmaster Tools
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