How reliable is ReturnPath inbox rate and why might it not correlate with open rates?
Summary
What email marketers say11Marketer opinions
Email marketer from Mailjet explains that factors like spam traps, blacklists, and authentication issues can affect email deliverability, leading to discrepancies between Return Path's reported inbox rates and actual open rates due to bad sending practices.
Marketer from Email Geeks suggests that if ISP weighting is different than what ReturnPath is using, it could skew the metrics. If an ISP is heavily represented in the ReturnPath list, but you have almost none of that ISP in your list, that could certainly skew the metrics in this fashion.
Email marketer from Reddit shares that different ISPs use varying spam filter algorithms. Return Path's results may not accurately reflect the filtering logic of all ISPs, leading to inconsistencies.
Marketer from Email Geeks explains that there's also a chance that the same 11-12% of recipients always open your messages. Therefore, mail to them is less likely to end up in the spam folder, even if your reputation drops a bit.
Email marketer from Litmus discusses that even if an email reaches the inbox, various factors like subject line relevance, preheader text, and sender recognition affect open rates, causing a disconnect between inbox placement and opens.
Email marketer from Email on Acid explains that seed list testing is limited. It provides a snapshot of deliverability but doesn't account for variations across all mailbox providers or user engagement.
Marketer from Email Geeks shares that any third party-reported inbox rate is unreliable, to varying degrees.
Marketer from Email Geeks agrees with Brad G and says that you may have a very engaged segment that will see the mail in their inbox; however, Open Rates aren't always the best indicator of response and suggests comparing clicks and conversions.
Email marketer from StackExchange shares that user engagement (opens, clicks, replies) impacts inbox placement. Low engagement may cause emails to land in spam, regardless of Return Path's initial assessment.
Email marketer from SocketLabs shares that sender reputation plays a significant role in inbox placement. A poor reputation can lead to inaccurate results in Return Path's inbox rate calculations if sender authentication is poor.
Email marketer from Gmass notes that deliverability testing with seed lists offers a limited view and may not accurately represent the experience of real subscribers with varying engagement levels.
What the experts say3Expert opinions
Expert from Word to the Wise explains that factors beyond Return Path metrics like content quality, sender authentication (SPF, DKIM, DMARC), and list hygiene significantly influence inbox placement, leading to discrepancies between reported inbox rates and actual open rates.
Expert from Spam Resource explains that seed list data, like that used by Return Path, provides a limited view of overall deliverability because it doesn't account for the diverse range of mailbox providers and filtering technologies that real users encounter.
Expert from Word to the Wise highlights the importance of feedback loops and complaint rates. High complaint rates can negatively impact deliverability, even if Return Path's seed-based testing suggests good inbox placement, leading to lower open rates.
What the documentation says5Technical articles
Documentation from SparkPost explains Seed list monitoring is a method for monitoring inbox placement and deliverability, by sending to a list of seed addresses and tracking placement.
Documentation from Validity Support explains that Return Path provides data on inbox placement, spam filtering, and missing mail to help diagnose deliverability issues. It monitors how mailbox providers handle your mail.
Documentation from Validity Support explains Return Path's seed data provide insight into your mail stream's performance at specific mailboxes and at specific mailbox providers. Seed-based results reflect mail landing in the inbox, spam folder, or missing altogether.
Documentation from Microsoft explains that sender reputation is a key factor in deliverability. Microsoft's SmartScreen filter uses reputation to determine whether to deliver messages to the inbox or junk folder, potentially impacting open rates.
Documentation from Google explains that even with good inbox placement, high spam complaint rates can suppress open rates. If users mark emails as spam, future emails might be automatically filtered, impacting opens even if they technically reach the inbox.