Why does a new ESP perform worse than an old ESP despite similar deliverability metrics?
Summary
What email marketers say9Marketer opinions
Email marketer from Sparkpost shares that the new ESP might have changes in template rendering or link tracking, which can affect user engagement. If emails look different or links are broken, users may be less likely to open or click.
Email marketer from Email Geeks asks if the postmaster tools have the same grade for the former IPs and new IPs, noting Gmail as a good indicator.
Email marketer from Gmass explains monitoring reputation using tools such as MultiRBL, Talos Intelligence or URIBL can show the differences between each ESPs reputation. This can help resolve deliverability issues.
Email marketer from Email Deliverability Forums responds that the underlying infrastructure of the new ESP might be less robust or optimized for deliverability than the old one. This can lead to slower sending speeds, connection problems with mailbox providers, and other issues that affect engagement.
Email marketer from Email Geeks asks if the email metrics have been pulled by domain to determine if the difference in performance is overall or tied to a specific mailbox provider.
Email marketer from Sendinblue shares that list hygiene practices significantly impact performance. If the old ESP had better list management, the new ESP might be sending to a list with more unengaged or problematic email addresses, leading to lower engagement.
Email marketer from Mailjet responds that a proper warmup process for the new ESP is critical. A gradual increase in sending volume allows mailbox providers to assess the sender's reputation. Rushing this process can negatively impact engagement metrics even if initial deliverability looks good.
Email marketer from NeilPatel.com explains that even with similar deliverability metrics, the new ESP may have a weaker sender reputation. This reputation impacts inbox placement, affecting opens and clicks. The quality of IP addresses used by the new ESP plays a crucial role.
Email marketer from Reddit shares that the new ESP might not have the same established feedback loops with mailbox providers as the old one. These loops provide data about spam complaints and other issues, allowing the ESP to adjust its practices. Without these feedback loops, the ESP might not be aware of deliverability problems.
What the experts say3Expert opinions
Expert from Word to the Wise explains that the problem may well be the IP address, the age of the IP address, whether it has been used for mail previously, and if so, what sort of mail. New ESPs often allocate fresh IPs that have no history, so you are starting from scratch - you have to build a reputation. But they also often allocate IPs that are relatively cheap, because they’ve been burned by others. If you get a burned IP you are starting out in a hole. Check the IP address reputation on a service like Talos, or Spamhaus.
Expert from Email Geeks shares that it's common for an old ESP to get higher clicks/signups than a new ESP, even without a firm explanation. Theories include different suppression criteria or platform-level reputation.
Expert from Spam Resource answers that volume and consistency can be a contributing factor. New ESPs will not have the history required to send the same volume, and they will require a new warmup which can lead to lower initial results. Monitor sending consistency and IP reputation closely.
What the documentation says4Technical articles
Documentation from Microsoft SNDS explains that sender health is evaluated by looking at complaint rates, spam trap hits, and other factors. A sudden increase in complaints or spam trap hits after switching ESPs can damage sender reputation, even if basic deliverability metrics look acceptable.
Documentation from AWS SES explains that sending limits and throttles can differ between ESPs. The new ESP might be imposing stricter limits, leading to delays in sending and affecting the timing of emails, which can impact engagement rates.
Documentation from Google explains that IP reputation directly affects email delivery to Gmail users. Even if overall deliverability seems fine, a poor IP reputation at Gmail can lead to emails landing in spam or being blocked, thus hurting performance.
Documentation from RFC explains that strict adherence to authentication standards (SPF, DKIM, DMARC) is critical. If the new ESP has misconfigured authentication, emails may pass basic deliverability checks but still be filtered or penalized by mailbox providers.