Summary
Mailbox providers (MBPs) use diverse methods for individual level filtering based on user interaction. Engagement metrics like opens, clicks, replies, and forwards are crucial indicators of email value, improving deliverability when positive and triggering filtering upon negative actions (spam complaints, unsubscribes). Different MBPs employ unique algorithms, necessitating a comprehensive approach combining technical compliance and engagement optimization. User feedback (marking as spam, not spam) informs Gmail and Yahoo's filtering, while Microsoft's SmartScreen considers a broad range of factors. Sender reputation (IP and domain) remains pivotal, sometimes overriding individual engagement signals. Consent is paramount; unsolicited emails face filtering. Feedback loops (FBLs) offer valuable complaint data for improved sender practices. Prioritizing relevant content and avoiding seed list dependence are also key.
Key findings
- Engagement is Key: Positive user engagement improves deliverability, while negative engagement leads to filtering.
- Algorithmic Diversity: MBPs use various filtering algorithms, requiring a multifaceted deliverability strategy.
- User Feedback Matters: Gmail and Yahoo leverage direct user feedback to refine their filters.
- Reputation Matters: Sender reputation (IP/domain) remains a crucial factor, sometimes overriding engagement.
- Consent is Paramount: Emails sent without explicit consent are highly likely to be filtered.
- Seed Lists Misleading: Seed lists provide an unreliable indication of deliverability; measure real user interaction.
- Content Relevance Impacts: Content Relevance impacts deliverability.
Key considerations
- Monitor and Optimize Engagement: Track engagement metrics and adjust sending practices to maximize positive interactions.
- Adhere to Technical Standards: Implement authentication protocols (SPF, DKIM, DMARC) and maintain a clean IP/domain reputation.
- Obtain Explicit Consent: Implement strict opt-in procedures to ensure recipients genuinely want to receive emails.
- Implement FBLs: Set up and actively monitor feedback loops to address spam complaints promptly.
- Focus on Content Relevance: Provide valuable and relevant content to encourage user interaction and avoid spam flags.
- Stay Updated: Continuously monitor email best practices as mailbox provider algorithms update.
What email marketers say
8 marketer opinions
Mailbox providers use user interaction data, such as opens, clicks, replies, forwards, spam complaints, and unsubscribes, to filter emails at an individual level. Positive engagement enhances sender reputation and improves deliverability, while negative interactions lead to stricter filtering. Different providers employ varying algorithms, necessitating a focus on both technical aspects and user engagement. Content relevance, feedback loops, and staying updated with best practices are crucial for maintaining good sender reputation and deliverability.
Key opinions
- Engagement Matters: Positive user engagement (opens, clicks, replies) improves sender reputation and deliverability.
- Negative Impact: Negative actions (spam complaints, unsubscribes, ignoring emails) negatively impact sender reputation and increase filtering.
- Algorithm Variety: Mailbox providers use different filtering algorithms; no single approach guarantees deliverability.
- Feedback Loops: Implementing feedback loops provides insights into spam complaints and helps address deliverability issues.
- Content Relevance: Relevant and interesting content is crucial to prevent users from ignoring or marking emails as spam.
Key considerations
- Monitor Engagement: Actively monitor user engagement metrics to identify and address potential deliverability problems.
- Technical Requirements: Understand and adhere to technical requirements (authentication, SPF, DKIM, DMARC) to improve deliverability.
- Stay Updated: Keep up with the latest best practices and algorithm changes implemented by mailbox providers.
- Content Strategy: Focus on creating valuable and relevant content that resonates with the audience.
- Implement FBLs: Set up feedback loops to receive and act on spam complaints promptly.
Marketer view
Email marketer from GlockApps explains that mailbox providers track user engagement metrics like opens, clicks, and replies. High engagement indicates that users find the emails valuable, improving deliverability. Low engagement or spam complaints can lead to filtering.
27 Jan 2025 - GlockApps
Marketer view
Email marketer from Reddit explains that different providers use different filtering algorithms, so you can't guarantee that any one method will always work. Understanding the technical requirements is still useful, but user engagement is also crucial.
15 Dec 2023 - Reddit
What the experts say
4 expert opinions
Mailbox providers (MBPs) prioritize user interaction data, such as reading, deleting, and marking emails as spam, when filtering emails. Focusing on inbox placement as a primary deliverability goal is misguided; genuine user engagement is more important. Seed lists are unreliable indicators of deliverability compared to real user behavior. Obtaining user consent is critical, as MBPs prioritize emails users have explicitly requested, and emails sent without consent are likely to be filtered based on low engagement or spam complaints.
Key opinions
- User Interaction Matters Most: User interaction (reading, deleting, marking as spam) significantly influences email filtering.
- Inbox Placement Misleading: Inbox placement is not a reliable measure of deliverability; focus on user engagement instead.
- Seed Lists Unreliable: Seed lists don't accurately reflect real user behavior, making them poor predictors of deliverability.
- Consent is Critical: Mailbox providers prioritize emails with explicit user consent.
Key considerations
- Focus on Engagement: Prioritize sending wanted mail and encouraging positive user interaction.
- Re-evaluate Metrics: Shift focus away from simply achieving inbox placement and towards measuring genuine user engagement.
- Obtain Explicit Consent: Ensure users have explicitly opted in to receive emails to improve deliverability.
- Avoid Unsolicited Mail: Refrain from sending emails to users who have not provided consent to avoid being filtered.
Expert view
Expert from Word to the Wise explains that inbox placement is not a measure of deliverability and should not be the primary goal. User interaction signals such as reading, deleting, and marking as spam significantly influence where messages land. Senders should focus on sending wanted mail.
4 Jun 2023 - Word to the Wise
Expert view
Expert from Email Geeks shares a link to a Word to the Wise article, suggesting it's the closest resource available regarding individual level filtering by MBPs: <https://wordtothewise.com/2018/12/never-100-inbox/>. She also suggests looking through her notes for deliverability discussions for potentially useful information.
15 Apr 2023 - Email Geeks
What the documentation says
5 technical articles
Mailbox providers like Gmail and Yahoo utilize direct user feedback, such as marking emails as spam or not spam, to train their filters and improve future message filtering. Microsoft's SmartScreen filter considers various factors, including email content, sender, recipient, and historical sender behavior. However, IP and domain reputation, as highlighted by Spamhaus, also plays a crucial role, potentially overriding individual user interactions if a sender's IP or domain is associated with spam activity. Feedback loops (FBLs), standardized by RFC Editor, enable senders to receive reports on spam complaints, improving deliverability and management practices.
Key findings
- User Feedback Drives Filtering: Gmail and Yahoo rely on user feedback (spam/not spam) to refine their filtering mechanisms.
- Holistic Evaluation: Microsoft's SmartScreen assesses content, sender, recipient, and historical data to identify suspicious emails.
- Reputation Overrides Interaction: IP/Domain reputation can override individual user interactions; a bad reputation leads to filtering regardless.
- FBLs Improve Practices: Feedback Loops (FBLs) are a key element to improving deliverability.
Key considerations
- Encourage User Feedback: Focus on the sending practices of other recipients.
- Monitor Sender Reputation: Maintain a clean IP and domain reputation to avoid being flagged as spam.
- Implement FBLs: Utilize feedback loops to address and resolve spam complaints effectively.
- Content Matters: Ensure email content adheres to best practices to avoid triggering spam filters.
Technical article
Documentation from Spamhaus explains that IP and domain reputation plays a vital role. If a sender's IP address or domain is associated with spam activity, mailbox providers are more likely to filter their emails, regardless of individual user interactions.
27 Jun 2021 - Spamhaus
Technical article
Documentation from Microsoft Learn explains that SmartScreen filter evaluates several things, including the content of the email, the sender, and the recipient, to decide if an email is suspicious. A large part of this is the historical behaviour of the sender and actions of other recipients.
14 Jun 2025 - Microsoft Learn
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