What are the best ways to measure email deliverability and inbox placement rates?

Key findings

• Seedlist utility: Seedlists are currently the most effective way to measure deliverability and inbox placement, providing measurable numbers for assessment. They are particularly useful for observing changes in your deliverability performance.
• Complementary metrics: Internal engagement metrics like opens, clicks, and conversion rates, especially when broken down by mailbox provider, offer crucial insights into actual inboxing. High bounce rates or low engagement indicators often signal deliverability issues.
• Postmaster tools: Leveraging free tools such as Google Postmaster Tools, Microsoft SNDS, and Sender Score, provides direct feedback on your sender reputation and how mailbox providers perceive your mail.
• Apple Mail Privacy Protection (MPP): MPP's image loading behavior can offer directional data on inbox placement for Apple users. Lack of MPP opens for a recipient who has them for other senders can indicate spam folder placement.

Key considerations

• Interpretation of seedlist data: Seedlist results should be interpreted carefully. They provide a general indication but don't always reflect the exact inbox placement rate for every individual recipient due to personalized filtering algorithms, such as those used by Gmail.
• Beyond delivery: Distinguish between email delivery (server acceptance) and inbox placement (landing in the primary inbox). A high delivery rate does not guarantee good inbox placement. For more detail, see Mailgun's explanation of inbox placement rate.
• Comprehensive monitoring: No single metric or tool provides a complete picture. The best approach involves combining data from seedlists, ESP analytics, postmaster tools, and potentially panel data to form informed decisions.
• Evolving landscape: The email deliverability landscape is constantly changing, with mailbox providers introducing new filtering mechanisms and data insights. Staying updated with these changes is crucial for accurate measurement.
• Technical setup: Proper email authentication (SPF, DKIM, DMARC) is foundational and impacts deliverability. Ensure your records are correctly configured. Our simple guide to DMARC, SPF, and DKIM can help.

Key opinions

• Seedlist as a baseline: Many marketers view seedlists as a fundamental tool for obtaining a measurable deliverability number, particularly for tracking changes over time.
• Leveraging existing data: The data already available from their Email Service Provider (ESP), such as opens, clicks, and conversions, is often considered the most valuable and free source of deliverability insights.
• Specific certifications: Some marketers highlight the benefit of certifications, like ReturnPath Certification, for providing concrete inbox placement data for major providers like Hotmail and Yahoo.
• Apple MPP's role: Apple's Mail Privacy Protection (MPP), by pre-fetching images, inadvertently offers a unique signal for inbox placement, as images are typically disabled in the spam folder.
• Holistic view: A comprehensive understanding requires combining various data sources, including seedlists, ESP metrics, and external reputation monitoring tools.

Key considerations

• Correlation vs. causation: Marketers must understand that while seedlist data is measurable, its direct correlation to actual inbox placement for individual recipients can vary and requires careful interpretation rather than being treated as a definitive inbox rate.
• Dynamic filtering: Email filtering is increasingly personalized. Marketers should be aware that their emails might land differently for different users even within the same domain, making a precise, universal inbox rate hard to pin down.
• Data segmentation: Segmenting open, click, and conversion data by individual mailbox provider, rather than just by domain, provides a more granular and actionable view of deliverability issues. This is a critical component of monitoring deliverability trends.
• Privacy shifts: Changes in privacy policies (e.g., Apple MPP) can both hinder and help deliverability measurement, creating a need for adaptive strategies.
• Beyond quantitative: While numbers are important, marketers also need to apply qualitative analysis and run email deliverability tests to diagnose issues.

Key opinions

• Seedlist as the best current method: Seedlists are widely considered the most effective method currently available for measuring deliverability and inbox placement rates, despite their limitations.
• Beyond seedlists: Experts emphasize the importance of looking at additional metrics like open rates, click-through rates, bounces, image loads, and rejections to get a more complete story of deliverability performance.
• Interpreting seedlist data: While seedlists provide measurable numbers, their correlation with actual inbox placement at a given mailbox provider (like Gmail's individualized filtering) requires careful interpretation rather than being treated as a precise inbox rate. Seedlist testing remains useful.
• Value of changes: Changes observed in seedlist numbers are highly significant and should be closely monitored as indicators of shifting deliverability.
• Mailbox provider transparency: There's an ongoing discussion among experts about the potential for mailbox providers to offer more direct, measured delivery data to senders in the future, which would significantly alter current measurement practices.

Key considerations

• Holistic data interpretation: Experts stress that no single tool or metric can provide a complete picture of deliverability. A holistic approach combining seedlist data, ESP analytics, postmaster tools, and potentially panel data is essential for informed decision-making.
• Leveraging free tools: Utilize free resources provided by major ISPs, such as Google Postmaster Tools, Sender Score, and Microsoft SNDS, as they offer invaluable direct feedback on your sender reputation.
• Inbox placement vs. delivery rate: It's crucial to understand the distinction: delivery rate indicates successful acceptance by the receiving server, while inbox placement rate signifies landing in the primary inbox, avoiding spam or junk folders.
• Proactive monitoring: Consistent monitoring of key metrics and proactive adjustments to sending practices are more effective than reactive troubleshooting after problems arise.
• Adaptability: The email landscape, particularly concerning privacy regulations and filtering algorithms, is constantly evolving. Experts advise senders to remain adaptable and informed about these changes to maintain optimal deliverability.

Key findings

• Delivery vs. inbox placement: Documentation consistently differentiates between email delivery (acceptance by the recipient's server) and inbox placement (landing in the primary inbox, not spam). True deliverability success is measured by inbox placement.
• Multi-factor influence: Achieving high inbox placement depends on numerous factors, including sender reputation, proper email authentication (SPF, DKIM, DMARC), content quality, and recipient engagement.
• Sender reputation is key: A strong sender reputation, built on consistent, positive sending practices, low complaint rates, and high engagement, is fundamental for bypassing spam filters and reaching the inbox.
• Monitoring tools: While challenging, a combination of various metrics and available tools can provide strong indicators of inbox placement, allowing senders to optimize their strategies.

Key considerations

• Technical compliance: Ensuring proper implementation of authentication protocols like SPF, DKIM, and DMARC is critical. Misconfigurations often lead to emails being flagged or rejected by receiving servers. Our guide on email testing to avoid deliverability issues can help.
• Filtering complexity: Mailbox providers utilize sophisticated and constantly evolving filtering algorithms. There is no single universal method to measure or guarantee inbox placement across all providers, necessitating continuous adaptation.
• Data integration: Successful measurement involves integrating data from various sources (e.g., ESP reports, ISP feedback loops, external testing) to form a comprehensive view of performance.
• Continuous optimization: Deliverability is not a one-time setup but an ongoing process of monitoring, analyzing, and optimizing sending practices to maintain a healthy sender reputation and consistent inbox placement.
• Blacklist avoidance: Documentation often emphasizes the detrimental effect of being listed on an email blacklist (or blocklist). Proactive monitoring and adherence to best practices are crucial to avoid such listings. Learn more in our guide on email blocklists.