Why have email open and CTR rates decreased after switching to Omnisend and emails are going to spam?
Michael Ko
Co-founder & CEO, Suped
Published 30 Apr 2025
Updated 18 Aug 2025
7 min read
Experiencing a sudden dip in email open and click-through rates, coupled with emails landing in spam folders, is a common and frustrating challenge, especially after migrating to a new email service provider (ESP) like Omnisend. Previously enjoying high engagement rates, like 65% open and 3.5% CTR with HubSpot, only to see them tank post-migration, signals significant deliverability issues. This problem is particularly acute when critical communications, such as invitations to exclusive events like a diamond trunk show, fail to reach their intended audience, directly impacting business outcomes.
The core of this issue often lies in the fundamental changes that occur when you switch email platforms. It's not just about moving your list, but also about how your sending infrastructure and domain reputation are perceived by mailbox providers. When emails start consistently hitting spam folders, it's a clear indication that your sender reputation is under scrutiny, affecting even your most engaged subscribers.
The immediate impact of an ESP migration
One of the most common reasons for a sudden drop in email engagement and an increase in spam placements after an ESP migration is an inadequate or absent IP warming process. When you switch platforms, you often move to new sending IPs. Even if your domain reputation is strong, these new IPs have no sending history, appearing as suspicious to mailbox providers.
This sudden change triggers spam filters, which are designed to protect recipients from unsolicited mail. Without a gradual ramp-up of sending volume, known as IP warming, your emails can be flagged, regardless of how engaged your audience was on your previous platform. This is a critical step that many overlook or underestimate, leading to significant deliverability challenges right out of the gate. For more insights, consider why marketing automation platform switches cause deliverability problems.
Additionally, the type of IP you're sending from matters. You might be on a shared IP address with Omnisend, where other senders' poor practices can negatively affect your reputation. Even if it's a dedicated IP, it still needs to establish its own reputation from scratch. This can lead to your emails being directed to the spam or junk folder, drastically reducing open and click-through rates, as observed in your case.
Technical authentication and domain reputation
Beyond IP reputation, email authentication protocols are paramount. When switching ESPs, it's crucial to ensure that your SPF, DKIM, and DMARC records are correctly configured for your new sending environment. Misconfigurations or incomplete setups can cause emails to fail authentication checks, leading mailbox providers to distrust your messages and route them directly to spam.
Before migration
Established reputation: Your domain and HubSpot's IPs had a long-standing history of good sending practices.
Authentication: DNS records like SPF, DKIM, and DMARC were properly aligned and validated over time.
Subscriber engagement: High open and CTR indicated strong recipient trust and inbox placement.
After migration
New IP reputation: Your new Omnisend sending IPs started with a neutral or unknown reputation.
Authentication issues: DNS records may not have been updated correctly or fully propagated.
Reduced inboxing: Emails flagged as spam, leading to lower open and click rates and missed opportunities, such as with a trunk show.
Monitoring your domain's reputation via tools like Google Postmaster Tools is essential. This platform provides insights into your sending reputation, spam rate, IP reputation, and authentication errors, particularly for emails sent to Gmail users. A sudden drop in reputation here is a strong indicator of underlying deliverability problems. You can learn more about Google Postmaster Tools V2 to get started. Also, checking for blocklist (or blacklist) status is critical, as a listing on a major blocklist can severely impede your ability to reach the inbox.
Content and list hygiene factors
While technical issues are often the primary culprits post-migration, content and list hygiene can also play a role or exacerbate existing problems. Mailbox providers analyze email content for spam triggers, which can include certain keywords, excessive use of capitalization, suspicious links, or poor HTML formatting. Even if your content hasn't changed, the new sending environment might be more sensitive to these factors.
Your email list's quality is also vital. Sending to an unengaged list, or one with a high percentage of inactive or invalid email addresses, can negatively impact your sender reputation. A high bounce rate, low engagement, or an increase in spam complaints (even from previously engaged users) will signal to ISPs that your emails are not desired, leading to more aggressive filtering. This is especially relevant if your list cleaning practices were not as rigorous before the migration.
It's important to differentiate between actual decreased engagement and reported metrics. Sometimes, a change in ESPs can alter how open and click rates are tracked or presented, but if your loyal customers are explicitly telling you they're finding your emails in spam, it's a genuine problem. For specific guidance on increasing email click-through rate you can follow a proven step-by-step guide.
Strategies to recover and maintain deliverability
To recover your email deliverability, the first step is to thoroughly investigate your new Omnisend setup. Confirm whether you are on a shared or dedicated IP and understand the warming process that was (or wasn't) undertaken. If an adequate warmup wasn't performed, you may need to scale back your sending volume and slowly increase it over time to build a positive reputation for your new IP.
Next, verify all your DNS records related to email authentication (SPF, DKIM, DMARC). Ensure they are correctly configured to reflect Omnisend's sending domains and IPs. An incorrect DMARC record, for example, could be explicitly telling mailbox providers to quarantine or reject emails that fail authentication. For a comprehensive check, use an email deliverability tester to diagnose any authentication issues. You can also monitor your DMARC reports to see where authentication failures are occurring. You can even check your blacklist status using monitoring services.
Beyond technical fixes, re-evaluate your email content and list management. Ensure your subject lines are engaging without being spammy, and your content provides clear value. Segment your audience and send targeted campaigns to highly engaged subscribers first, gradually expanding to a broader audience as your reputation improves. Regularly clean your list to remove inactive or problematic addresses, as this will prevent further damage to your sender score. Implementing these measures can help you get back on track to improve email deliverability.
Views from the trenches
Best practices
Ensure a thorough IP warming process is implemented when migrating ESPs, gradually increasing sending volume over time.
Verify all email authentication records (SPF, DKIM, DMARC) are correctly configured for your new ESP.
Proactively monitor your domain reputation using tools like Google Postmaster Tools for major mailbox providers.
Regularly clean your email list to remove inactive, invalid, or unengaged subscribers to maintain list quality.
Focus on sending highly relevant and engaging content to improve positive recipient interactions and avoid spam complaints.
Common pitfalls
Skipping or rushing the IP warming process after migrating to a new email service provider.
Failing to update or incorrectly configuring email authentication records for the new sending platform.
Not monitoring sender reputation metrics, leading to undetected deliverability issues and spam placements.
Continuing to send to a large list of unengaged or inactive subscribers, which can harm sender reputation.
Ignoring early signs of decreased open rates or increased spam complaints after a platform switch.
Expert tips
Use a DMARC policy of p=none initially to gather reports and monitor authentication alignment without affecting delivery.
Segment your most engaged subscribers and send to them first during the initial phases of IP warming.
Actively track bounce rates, spam complaint rates, and unsubscribe rates in addition to opens and clicks.
If using a shared IP, understand the shared IP's reputation and how it is managed by your ESP.
Consider a phased migration approach instead of a hard cut-over to minimize disruption to deliverability.
Marketer view
Marketer from Email Geeks says: A proper cut-over and warmup process is essential when changing domains or IPs. This contributes significantly to immediate deliverability.
2024-01-20 - Email Geeks
Expert view
Expert from Email Geeks says: When switching ESPs, IP changes normally occur. This is a primary factor in reputation reset and deliverability challenges.
2024-01-21 - Email Geeks
Moving forward: regaining your inbox presence
The sharp decline in email open and CTR rates, and the increased spam folder placement after switching to Omnisend, is a clear indication of a disrupted sender reputation. This disruption is primarily due to the change in sending IPs and the subsequent need to re-establish trust with mailbox providers.
Addressing this requires a multi-faceted approach focusing on proper IP warming, meticulous email authentication setup, continuous monitoring of your domain's reputation, and maintaining excellent list hygiene and content quality. By systematically tackling these areas, you can recover your deliverability and ensure your valuable communications reach the inbox.
Remember that deliverability is an ongoing effort. Even after resolving immediate issues, consistent monitoring and adherence to best practices are key to maintaining a strong sender reputation and maximizing the impact of your email campaigns. For more insights on this issue, explore our article on why your email open rate has decreased recently.
Omnisend. Previously enjoying high engagement rates, like 65% open and 3.5% CTR with 
HubSpot, only to see them tank post-migration, signals significant deliverability issues. This problem is particularly acute when critical communications, such as invitations to exclusive events like a diamond trunk show, fail to reach their intended audience, directly impacting business outcomes.
