Why do marketing automation platform switches cause drop in email open rates?
Matthew Whittaker
Co-founder & CTO, Suped
Published 23 May 2025
Updated 30 Sep 2025
7 min read
Migrating marketing automation platforms (MAPs) is a significant undertaking, and it is not uncommon to see a sudden drop in email open rates and unique click-through rates (CTRs) immediately after the switch. Even if your SPF and DNS entries appear correct and you are using shared IP addresses, there are several subtle yet powerful factors that can impact your email deliverability and reported metrics.
The core issue often boils down to how different platforms handle sending infrastructure, reputation management, and even the very definition of an 'open' or 'click'. Understanding these underlying differences is crucial for diagnosing and rectifying the drop in your email engagement. We'll explore these common causes and provide actionable insights to help restore your rates.
Calculation discrepancies
One of the most frequent reasons for a perceived drop in open rates after switching platforms is simply a difference in how these platforms calculate and report metrics. While the raw number of opens might be similar, the reported rate can vary significantly.
Old platform: Marketo
Marketo might calculate open rates using 'emails sent' as the denominator, which is a common practice. Additionally, it might have a mechanism to count clicks as opens if the open tracking pixel failed, inflating the reported open rates slightly.
Denominator: Often uses 'emails sent' for open rate calculations.
Click-to-Open: May count clicks as opens if the tracking pixel doesn't fire.
Engagement definition: Potentially more generous in how it defines and attributes an 'open'.
New platform: Pardot
Pardot, or other platforms, might use 'emails delivered' as the denominator, which is a more accurate reflection. They might also be stricter about only counting an actual pixel load as an open, leading to lower reported rates.
Denominator: Often uses 'emails delivered' for open rate calculations.
Click-to-Open: May not count clicks as opens, requiring explicit pixel load.
Engagement definition: Potentially more conservative in its definition of an 'open'.
As noted on a HubSpot community discussion, differences in metric calculation are a common point of confusion. It's crucial to understand these variations when comparing performance across platforms. A detailed audit of both platforms' reporting methodologies can reveal if the drop is merely a statistical artifact rather than a true decline in engagement.
Another factor is the emergence of privacy features like Apple Mail Privacy Protection (MPP), which pre-fetches emails and records them as 'opened' even if the user hasn't seen them. This has made open rates less reliable, pushing marketers to focus more on clicks. If your new platform filters out these 'proxy opens' more aggressively, your reported open rates will naturally appear lower. This is a key reason why you might see your email engagement decrease after migrating email service providers.
Sender reputation and IP warming
Even if you are using shared IP addresses, a platform switch means you are sending emails from new sending IPs and potentially a new sending domain. This resets your sender reputation, which is critical for getting into the inbox. Internet Service Providers (ISPs) like Google and Yahoo rely heavily on this reputation to filter incoming mail.
A new platform's shared IP pool, while generally robust, might not have the same level of established trust with all ISPs as your previous platform's. This is particularly true if your old platform had strong domain reputation. Your new IP addresses need a 'warming up' period to build their own reputation. During this time, ISPs are more likely to filter your emails to the spam folder or even block them, leading to lower open rates. You might also find yourself on a blocklist if the shared IP pool has been abused by other senders.
The danger of cold IPs
Even with shared IP pools, a new platform essentially starts you with a 'cold' sending reputation. ISPs analyze sending patterns, volume, and engagement from new IP addresses very closely. A sudden surge in volume from a new IP range, even if shared, can trigger spam filters. This can cause email deliverability issues like lower inbox placement, directly impacting your open rates.
Additionally, if your new marketing automation platform introduces changes to your sending domain's email authentication, such as SPF or DKIM records, this can also impact deliverability. While you mentioned your SPF and DNS entries are correct, ensuring DMARC is properly configured and monitored is crucial during a migration to protect your domain's reputation. Tools like Suped can provide valuable DMARC monitoring and reporting to ensure your emails are consistently authenticated and reaching inboxes effectively.
Technical template and tracking differences
Technical implementation differences between marketing automation platforms can significantly affect open rates, even when content remains the same. One subtle but impactful factor is the tracking pixel used to detect opens. If the new platform's email template adds more HTML or CSS code, it can lead to email clipping issues in clients like Gmail.
When an email is clipped, the tracking pixel at the bottom might not load unless the recipient clicks 'view entire message'. This can cause a noticeable drop in reported open rates, even if recipients are seeing and engaging with the top portion of your email. This is particularly relevant if you've recently experienced sudden email open rate drops and are struggling to pinpoint the cause.
Beyond clipping, ensure that your email templates are fully responsive and render correctly across all major email clients and devices. Poor rendering can lead to a negative user experience, discouraging opens and clicks, thus lowering engagement. Consider performing an email deliverability test to verify how your new templates are performing.
List hygiene and content triggers
The quality of your email list plays a significant role in open rates. When migrating platforms, it's a prime opportunity to re-evaluate your list hygiene. If you moved a 'cold' or unengaged list to a new platform without proper re-engagement, you might see a natural drop in open rates as these subscribers are less likely to open your emails regardless of the sending platform.
A new platform might also have more stringent spam filter rules or be more sensitive to specific keywords, content patterns, or email templates that were tolerated by your previous provider. What worked before might now trigger spam filters, pushing more emails to junk folders and diminishing visibility. This can explain why your emails are going to spam post-migration.
Best practices for list hygiene and content
Segment your list: Isolate highly engaged subscribers from less active ones. Focus on warming up your new platform with engaged segments first.
Re-engage cold subscribers: Implement specific re-engagement campaigns before sending to your entire list from the new platform.
Review content: Ensure your content adheres to general best practices for deliverability, avoiding spammy triggers.
Monitor blocklists: Regularly check if your sending IPs or domain are on any email blocklists (or blacklists). You can use a blocklist checker.
A thorough list cleansing process before migrating is often overlooked. Removing inactive or invalid email addresses can significantly boost your deliverability and reported open rates on the new platform, as you will be sending to a more receptive audience. This proactive approach helps in maintaining a healthy sender reputation.
Views from the trenches
Best practices
Always compare email metrics from different platforms by understanding their unique calculation methodologies.
Segment your audience by engagement levels and warm up new sending IPs gradually with your most engaged subscribers.
Thoroughly review your email templates for excessive code or design elements that could lead to clipping in email clients.
Implement strong email authentication (SPF, DKIM, DMARC) and monitor reports from the new platform diligently.
Common pitfalls
Assuming open rates are calculated identically across all marketing automation platforms, leading to misleading comparisons.
Migrating an entire cold list to a new platform without prior re-engagement, impacting initial sender reputation.
Overlooking subtle changes in email template HTML that can cause emails to be clipped, affecting open tracking.
Neglecting to monitor DMARC reports, which can indicate deliverability issues or authentication failures with the new setup.
Expert tips
Actively monitor specific inbox providers like Google and Microsoft to identify any prevalent deliverability issues.
Ensure that any email clicks are also consistently registered as opens, if that aligns with your desired reporting.
Regularly check your sending domains against public and private blocklists (blacklists) to ensure your reputation remains clean.
Understand the impact of privacy features like Apple MPP on open rates and adjust your measurement strategy accordingly.
Marketer view
A marketer from Email Geeks says they saw a drop-off in open rates after switching from Marketo to Pardot, but the sending domain had not changed.
2020-10-27 - Email Geeks
Marketer view
A marketer from Email Geeks shared that comparing open rates between platforms can be misleading due to differences in how the numbers are calculated. One platform might use 'sent' as the denominator, while another uses 'accepted' or 'delivered'.
2020-10-27 - Email Geeks
Restoring your email engagement
A drop in email open rates after a marketing automation platform switch can be a multifaceted problem, often stemming from a combination of calculation discrepancies, sender reputation challenges, and technical implementation differences. It's rarely a single, simple cause.
To effectively troubleshoot, begin by scrutinizing how both your old and new platforms define and measure open rates. Simultaneously, focus on gradually warming up your new sending infrastructure and ensure your email authentication, particularly DMARC, is robust. Paying close attention to list hygiene and testing your email templates for clipping issues will also contribute significantly to restoring your desired engagement levels.
Even if you are using shared IP addresses, a platform switch means you are sending emails from new sending IPs and potentially a new sending domain. This resets your sender reputation, which is critical for getting into the inbox. Internet Service Providers (ISPs) like Google 
and Yahoo rely heavily on this reputation to filter incoming mail.
