Why do email engagement metrics change when I switch ESPs?

Different Email Service Providers (ESPs) have unique ways of tracking and reporting metrics like opens and clicks, often filtering out bot activity or pre-fetching differently. This can lead to a perceived drop in engagement that doesn't necessarily mean fewer actual human interactions.

How long does it take for a new sending IP or subdomain to build reputation with mailbox providers?

It can take several months to a year for a new IP address or subdomain to fully build trust and stabilize its reputation with major mailbox providers like Google and Microsoft . They observe a "wait-and-see" period to monitor sending behavior.

Should I reduce my sending volume or segment my list more tightly after migrating ESPs?

Yes, especially if you observe a genuine drop in traffic or conversions. Start by sending to your most engaged segments (e.g., recent clickers) and gradually expand volume. This helps build positive sending reputation with your new infrastructure.

What role does content and audience relevance play in post-migration engagement drops?

Even with a healthy sender reputation, if your email content, subject lines, or frequency don't resonate with your audience, engagement will decline. Recipient fatigue is common, and continuous optimization of your messaging is crucial.

How can I differentiate between a reporting issue and a true deliverability problem?

If only open rates drop but traffic and conversions remain stable, it might be a reporting discrepancy. However, if traffic, conversions, and other key performance indicators also decline, it indicates a true deliverability or engagement problem that needs deeper investigation.

Is it normal for emails to land in the promotions tab after an ESP migration?

Yes, it is common for emails to initially land in the promotions tab (for consumer mailboxes like Gmail ) after an ESP migration, especially with changes to sending infrastructure. This can contribute to lower reported open rates as promotions tab emails are often not pre-fetched in the same way as those in the primary inbox.

Why did email engagement decrease after migrating email service providers? - Troubleshooting - Email deliverability - Knowledge base

When you switch email service providers (ESPs), it is common to see a puzzling drop in engagement metrics like open and click rates. This can be alarming, especially when your email list hygiene is strong and your domain reputation appears unaffected. The immediate reaction is often to assume a deliverability issue, but the reality is frequently more nuanced.

I've observed this scenario multiple times, where a migration from one ESP to another, even with proper IP warming and list scrubbing, leads to significant dips in engagement. It's a complex challenge, as many factors beyond typical deliverability metrics come into play. Understanding these underlying causes is key to diagnosing and resolving the perceived decline in performance.

How reporting metrics and email clients vary

When migrating ESPs, a primary reason for a perceived drop in email engagement is how different platforms measure and report opens and clicks. Each email service provider has unique methodologies for filtering out non-human interactions, such as bot opens and clicks. This means that a decrease in reported engagement might not reflect a true decline in human interaction, but rather a change in how the data is filtered and presented. For instance, the number of emails that load images (which count as opens) can vary greatly.

Mailbox providers also play a significant role.

Google, in particular, may not immediately pre-fetch images when it detects infrastructure changes or a new subdomain. This can artificially lower reported open rates, as the image (and thus the "open") is only loaded if the recipient actively opens the email, rather than being pre-fetched in the background. If a significant portion of your audience uses

Google services, this effect can be quite pronounced. This phenomenon can make it seem like your emails are performing worse, even if they are landing in the inbox. You can find more information about why email open rates are still relevant by looking at external sources like Salesforce's blog.

Metric	Old ESP (Salesforce Marketing Cloud)	New ESP (Hubspot)
Open rates	Includes many bot opens, higher pre-fetching.	More aggressive bot filtering, less pre-fetching.
Click rates	May include bot clicks, higher reported clicks.	Stricter filtering, potentially lower actual clicks.
Inbox placement	Consistent inbox delivery, minimal promotions tab.	Initial shifts to promotions tab common, especially for Gmail.

Ultimately, if your emails are reaching the inbox and spam complaints remain low, the drop in opens might primarily be a reporting discrepancy rather than a fundamental deliverability problem. It is crucial to look beyond raw metrics and assess actual business outcomes, like traffic to your website or conversions, to get a clearer picture. For example, if web traffic from email campaigns has also dropped, it indicates a real engagement issue that needs to be addressed. This situation is particularly relevant when considering how email engagement boosts deliverability.

Sender reputation and ip warming challenges

Even with proper IP warming, transitioning to a new ESP (or a new IP address) means building a fresh sender reputation with Internet Service Providers (ISPs). While your root domain's reputation might be strong from years of sending, the new sending IP and subdomain often start with a neutral, rather than positive, reputation. ISPs like

Outlook (or

Microsoft 365) observe a "wait-and-see" period for new sending infrastructures. During this time, they closely monitor sending behavior, engagement, and complaint rates. This can lead to temporary throttling or even more aggressive filtering, impacting your inbox placement and, consequently, engagement. For example, a previous client migrating to Klaviyo experienced similar engagement drops.

It can take a significant amount of time, sometimes up to a year, for a new IP or subdomain to fully earn the trust of major mailbox providers. This "holding pattern" means that even if you followed all the warming guidelines, ISPs might still place your emails under evaluation for an extended period. During this phase, it's critical to maintain consistent, high-quality sending practices. This cautious approach by ISPs is designed to prevent spammers from quickly establishing new sending infrastructure. You can learn more about how long it takes to recover domain reputation.

The danger of over-sending

A common pitfall is to send to too broad an audience too soon on a new IP, even if the list was engaged on the old platform. It's often beneficial to start with your most engaged segments (e.g., recent clickers, then recent openers) and gradually expand volume. If you see a dip in engagement, it might be necessary to temporarily dial back your sending volume to the segments that were performing well, then slowly re-introduce broader audiences. You don't get an automatic "fresh start" with a new IP and subdomain, even if your existing brand reputation is solid. For a deeper dive, read about how email blacklists actually work.

Audience engagement and list management

Beyond technical factors, declining email engagement after an ESP migration can also stem from shifts in audience behavior or issues with list management. Even if your list was thoroughly scrubbed before the move, maintaining optimal list hygiene on an ongoing basis is paramount. If you've been sending to a broad segment, such as contacts who have engaged within the last six months, it might be too wide for a new IP's initial reputation-building phase. Mailbox providers prioritize recent and positive engagement signals.

Recipient fatigue can also play a role, regardless of an ESP migration. In today's crowded inboxes, subscribers are bombarded with emails. If your content, subject lines, or frequency don't consistently resonate, engagement will naturally decline. Even for valuable content like event invitations or informative newsletters, if the perceived value has diminished or the competition for attention has increased, opens and clicks will suffer. This is why email frequency is a critical factor impacting engagement.

Consider segmenting your audience more aggressively, especially during and after a migration period. Focusing on those who have shown very recent engagement (e.g., within the last 30-90 days) can help boost initial positive signals to ISPs. While removing less engaged contacts entirely might be drastic, reducing sending frequency to them or placing them on re-engagement campaigns can be a more strategic approach. Continuously evaluating your list health and refining your engagement thresholds is crucial for sustained deliverability and engagement, as outlined in guides like how to improve domain reputation using Google Postmaster Tools.

Proactive strategies for recovery

Diagnosing the precise cause of an engagement drop requires a multi-faceted approach. First, segment your engagement data by domain, especially focusing on large mailbox providers like

Google,

Microsoft, and

Yahoo. This will help determine if the drop is across your entire database or concentrated with specific providers. If a significant portion of your unengaged contacts are from a particular domain, it suggests a targeted deliverability or reputation issue with that provider, rather than a universal reporting change. You can also monitor your DMARC reports for further insights into delivery issues.

Review your email authentication records (SPF, DKIM, and DMARC) carefully after the migration. While often configured by the new ESP, even minor misconfigurations can impact deliverability. Verify that all records are correctly published for your new sending subdomain and that they align properly. Using a DMARC monitoring tool can help you identify any authentication failures that might be contributing to poor inbox placement. A simple guide to DMARC, SPF, and DKIM can assist in this verification.

If real engagement (traffic, conversions) has declined, not just reported metrics, then you might need to adjust your sending strategy. Re-evaluate your content, subject lines, and calls-to-action to ensure they are compelling. Consider A/B testing different approaches to see what resonates with your audience on the new platform. It's also vital to consistently check for any blocklist (or blacklist) listings. Tools that provide blocklist checking and blocklist monitoring can help you stay on top of any potential reputation issues. Maintaining good list hygiene by suppressing inactive subscribers is always a best practice to protect your sender reputation.

Final thoughts

A decrease in email engagement after migrating ESPs is a common and often multifaceted problem. It can be attributed to differences in how platforms report metrics, the time required for new IPs and subdomains to build trust with ISPs, and shifts in audience engagement or content relevance. While a perceived drop might sometimes be a reporting artifact, a real decline in traffic and conversions indicates deeper issues that require attention.

The key to overcoming these challenges lies in a thorough investigation of both technical and strategic elements. By understanding how different ESPs handle metrics, patiently building sender reputation through targeted sending, and continually optimizing your content and list segmentation, you can regain and even improve your email engagement over time. Remember to document all changes and monitor a wide range of metrics, not just opens, to accurately gauge performance.

Views from the trenches

Best practices

Segment your audience based on recent engagement to build trust with a new sending infrastructure.

Regularly review and adjust your sending volume during the initial ramp-up period on a new ESP.

Document the exact date of your ESP migration and any related infrastructure changes for historical context.

Analyze engagement data by specific mailbox provider, especially for large ones like Google and Microsoft.

Focus on key performance indicators beyond open rates, such as traffic and conversions, to assess true impact.

Common pitfalls

Assuming a new ESP automatically inherits your old sender reputation.

Sending to your entire active list too soon after a migration, even if it was performing well before.

Over-relying on reported open rates without considering ESP-specific bot filtering or pre-fetching differences.

Failing to communicate potential temporary metric dips to higher-ups before migration.

Not adjusting content or sending frequency based on observed engagement patterns on the new platform.

Expert tips

Monitor Google Postmaster Tools closely for insights into IP and domain reputation.

Consider that some B2B anti-spam filters might be processing links differently, affecting reported clicks.

Be patient, as it can take up to a year for a new sending infrastructure to fully stabilize with major ISPs.

If true engagement (conversions/sales) has dropped, then a tighter engaged segment is often necessary.

Don't immediately cut off less engaged recipients; consider reducing frequency or running re-engagement campaigns.

Expert view

Expert from Email Geeks says: Different ESPs (Email Service Providers) filter non-human interactions like bot opens and clicks in varied ways, so a drop in engagement might solely be a change in how data is reported.

June 24, 2024 - Email Geeks

Expert view

Expert from Email Geeks says: Google often doesn't immediately pre-fetch images when infrastructure changes or new subdomains are used, leading to reported data changes rather than actual engagement drops.

June 24, 2024 - Email Geeks