Summary
The question of whether inbox providers (ISPs and mailbox providers like Gmail, Outlook, Yahoo, etc.) share email deliverability data with each other is a common one among senders. While it might seem logical for them to share comprehensive data to improve spam filtering, the reality is more nuanced. Generally, explicit, detailed deliverability data (like your specific open rates or spam complaint rates at their service) is not directly exchanged between these providers due to privacy concerns and competitive interests. However, there are instances where they share aggregated threat intelligence, particularly regarding malicious actors, botnets, and known spam campaigns.
Key findings
- Limited direct sharing: Inbox providers typically do not share granular deliverability metrics, such as individual sender reputation scores or specific inbox placement rates, with competing providers. Each provider maintains its own proprietary algorithms and data sets.
- Threat intelligence sharing: There are established industry forums and partnerships (like the Messaging, Malware and Mobile Anti-Abuse Working Group, M3AAWG) where providers collaborate to share information on emerging threats, botnet activity, and major spam campaigns. This helps them collectively combat widespread abuse.
- Privacy concerns: Sharing detailed user engagement data or sender performance metrics among providers would raise significant privacy issues and could be seen as anti-competitive.
- Independent filtering: Each major mailbox provider develops and refines its own unique spam filters and reputation systems, tailored to its user base's behavior and preferences. Learn more about how these systems function in our guide on how email deliverability works.
- Reputation impacts: While direct sharing is minimal, a sender's poor practices (e.g., high spam complaints, sending to old lists) can independently harm their reputation across multiple providers, leading to similar deliverability issues (such as blocklisting or going to the spam folder) because each provider observes the same negative patterns. This is often misunderstood as direct data sharing. We dive into how to monitor and improve your standing in our guide to understanding your email domain reputation.
Key considerations
- Focus on universal best practices: Since each provider evaluates independently, adhering to general email marketing best practices (engagement, list hygiene, authentication) is crucial for consistent performance across the board. Klaviyo provides a useful overview on understanding email deliverability.
- Monitor per-provider performance: Even if providers don't share data, your performance can vary significantly between them. Tools like Google Postmaster Tools (for Gmail) and Microsoft SNDS (for Outlook/Hotmail) offer insights specific to those domains.
- Understand linked systems: Some legacy domains or smaller ISPs might outsource their email infrastructure or filtering to larger providers (e.g., Yahoo handling AT&T email in the past). Improvements with the primary provider would then naturally affect the linked domains.
- Attribute changes carefully: When analyzing deliverability shifts across multiple domains, consider internal changes in your sending strategy, audience segmentation, or content, as these are often the root cause of observed performance variations.
What email marketers say
Email marketers often observe shifts in deliverability across multiple inbox providers simultaneously, leading to speculation about data sharing. While the consensus is that direct sharing of granular deliverability data is minimal, marketers frequently note that improving practices for one major provider can seemingly have a positive ripple effect on others. This isn't necessarily due to direct data exchange but rather because good sending practices are universally recognized by diverse filtering systems.
Key opinions
- Indirect correlation: Many marketers report that optimizing for one major ISP (like Gmail or Yahoo) often leads to improved metrics across other domains, even without explicit data sharing. This suggests that robust sending practices benefit all providers.
- Audience adjustments matter: Refining audience segments to target more engaged subscribers can significantly boost overall open rates and positive engagement metrics, which are factors independently considered by all inbox providers, improving deliverability for everyone. We have a guide on how internet service providers track email engagement.
- Confusion around causality: Marketers sometimes attribute broad deliverability improvements to ISP data sharing when, in fact, changes in their own sending behavior or audience quality are the more likely underlying cause. This highlights the importance of precise data analysis.
- Holistic deliverability view: The focus should always be on maintaining a strong sender reputation across all channels rather than hoping for data sharing between providers. A healthy email program benefits all destinations.
Key considerations
- Segment by domain: Marketers should analyze their deliverability and engagement metrics broken down by individual domain (e.g., Gmail, Yahoo, Outlook) to identify specific areas for improvement, even if overall trends seem positive.
- Review internal changes: Before concluding that ISPs are sharing data, thoroughly investigate any recent changes in your email program, such as list segmentation, content strategy, sending volume, or infrastructure. Often, these internal shifts explain observed deliverability improvements.
- Engagement is key: ISPs prioritize user engagement. Positive interactions (opens, clicks, replies) signal to all providers that your mail is wanted, which is independently assessed by each. Email engagement directly impacts deliverability across the board.
- Monitor blocklists (blacklists): While direct deliverability data isn't shared, blacklists and blocklists are public or semi-public lists that many providers consult. Monitoring your presence on these lists (e.g., via a blocklist checker) is critical because an issue with one can quickly affect others.
Marketer view
Email marketer from Email Geeks shared an observation that after adjusting their audience for Gmail and Verizon domains to a smaller, more active group, not only did open rates for those specific domains increase, but they also saw a rise in open rates for other domains like Comcast, Hotmail, and AT&T. This occurred without other content or reputation changes. The marketer initially wondered if this suggested data sharing between inbox providers.
Marketer view
Email marketer from Beehiiv Blog asserts that email providers have become very skilled at distinguishing between different senders, even those sharing an IP pool. This means that a sender's individual reputation and practices are paramount, rather than being broadly grouped.
What the experts say
Experts in email deliverability, many of whom have direct relationships with inbox providers and anti-spam organizations, consistently affirm that while collaborative efforts exist to combat widespread threats, individual deliverability data is not shared among competing ISPs. They emphasize that each provider operates with its own unique filtering criteria and user feedback loops, making sender reputation a distinct metric for each.
Key opinions
- Independent assessments: Experts confirm that mailbox providers largely evaluate senders independently. A sender's positive performance with one ISP does not automatically guarantee good standing with another.
- Threat data vs. delivery data: While sensitive, aggregated data about malicious actors and botnets is shared for security purposes, specific deliverability performance data (like unique opens or spam rates for legitimate senders) is generally not exchanged. This distinction is crucial.
- Privacy implications: Sharing user engagement data across competing providers would raise significant privacy concerns and goes against the principle of independent user data management.
- Focus on user experience: Each ISP's primary goal is to provide the best possible experience for its users, which means filtering mail based on its own user's interactions and security assessments, rather than relying on another provider's judgment.
Key considerations
- Direct engagement with postmasters: If you encounter deliverability issues with a specific provider, the most effective approach is to engage directly with their postmaster resources. We provide advice on how to contact mailbox providers for deliverability issues.
- Holistic deliverability strategy: Instead of looking for a singular reason across providers, adopt a comprehensive deliverability strategy that addresses common requirements like sender authentication (SPF, DKIM, DMARC) and positive user engagement. Our simple guide to DMARC, SPF, and DKIM can help.
- Industry knowledge: Stay informed about industry trends and general best practices as they evolve, as these often influence filtering decisions across multiple providers. Mailsoar offers insights into how major mailbox providers behave.
- Avoid assumptions: Do not assume deliverability changes across providers are due to data sharing. Always seek concrete evidence from your own sending data and postmaster tools.
Expert view
Email expert from Email Geeks, who has been engaging with ISP filter developers for over 20 years, firmly states that direct sharing of individual sender deliverability data is not happening. They relayed a common sentiment from ISPs: 'just because X likes your mail doesn't mean we do,' highlighting the independent nature of their filtering decisions.
Expert view
Email expert from SpamResource explains that ISPs might use shared data, but it typically concerns threat intelligence rather than specific sender delivery metrics. This collaboration is focused on combating widespread malicious activity, not on exchanging insights about legitimate sender performance.
What the documentation says
Official documentation from major mailbox providers and industry standards bodies rarely (if ever) mentions explicit sharing of granular deliverability performance data between competing entities. Instead, the focus is on independent assessment criteria, adherence to open standards, and collaborative efforts to combat abuse. While aggregate threat intelligence might be shared, individual sender reputations and specific inbox placement decisions remain proprietary.
Key findings
- Emphasis on independent reputation: Documentation from providers like Gmail and Outlook (via Google Postmaster Tools and SNDS) details how they calculate sender reputation based on their own internal metrics (e.g., spam complaint rates, direct user feedback), with no mention of cross-provider data exchange for this purpose.
- Standards and protocols: Documentation focuses on adherence to open email standards (RFCs) and authentication protocols like SPF, DKIM, and DMARC, which allow each provider to verify sender legitimacy independently. Our article on what RFC 5322 says provides further insight.
- Abuse reporting: While specific delivery data isn't shared, platforms like AbuseIPDB or Spamhaus maintain public blacklists (blocklists) of known malicious IPs and domains. These are compiled from various sources, including direct reports and honeypots, and are widely consulted by ISPs.
- Collaborative anti-abuse efforts: Organizations like M3AAWG facilitate information sharing on security threats and best practices, but this is distinct from sharing commercial deliverability performance data for individual senders.
Key considerations
- Review postmaster guidelines: Always consult the official postmaster guidelines for each major inbox provider (e.g., Gmail, Outlook, Yahoo) to understand their specific requirements and recommendations for senders. These are the primary sources for deliverability best practices.
- Understand feedback loops: Many providers offer feedback loops (FBLs) to allow senders to receive reports on spam complaints from their users. This is a direct, albeit one-way, sharing of data for deliverability improvement. Learn more about how technical email deliverability factors into this.
- Implement DMARC: DMARC (Domain-based Message Authentication, Reporting & Conformance) is an industry standard that allows senders to receive aggregate reports from participating mailbox providers. While not individual delivery data, these reports offer valuable insights into authentication failures and potential abuse, helping you improve your overall email ecosystem. Our guide to understanding DMARC reports is a good starting point.
Technical article
Documentation from Klaviyo Help Center on understanding email deliverability notes that monitoring your deliverability performance over time is essential for understanding how inbox providers perceive your brand as a sender. This implies an independent assessment by each provider, rather than a shared global score.
Technical article
Documentation from Mailjet's 'Road to Inbox' guide states that mailbox providers aim for user-generated spam complaints to remain below 0.1%, with a critical threshold often at 0.3% (one complaint per 1,000 emails delivered). This threshold is a universal metric observed by providers, driving their independent filtering decisions.
Related resources
6 resources
Related pages
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What factors influence email deliverability and how does SenderScore work?
How do Internet Service Providers track email engagement and its impact on deliverability?
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A practical guide to understanding your email domain reputation
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Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
