Why is it harder to rebuild domain/IP reputation after switching from Mailchimp?
Michael Ko
Co-founder & CEO, Suped
Published 20 Jul 2025
Updated 17 Aug 2025
6 min read
Moving an email program from a platform like Mailchimp to a new email service provider (ESP) can present unique challenges, especially when it comes to maintaining and rebuilding your domain and IP reputation. Many businesses find that what seemed like a straightforward transition quickly becomes a battle for inbox placement.
The difficulty often stems from a combination of factors, including the inherited reputation of the domain, the new ESP's infrastructure, and the evolving rules set by major mailbox providers. It is not uncommon for domain or IP reputation to start low, or even drop to 'bad', soon after a switch.
The evolving landscape of email reputation
The email deliverability landscape is constantly evolving, with mailbox providers like Google and Yahoo implementing stricter policies to combat spam and improve user experience. This means that sender reputation is no longer just about your IP address, but increasingly about your domain's sending history and engagement metrics.
When you use a large, established ESP like Mailchimp, you often benefit from their pooled IP reputation. While your domain builds its own reputation, a new dedicated IP or a new set of shared IPs at a different ESP will need to build trust from scratch. This can feel like starting over, even if your domain has a long history. You can learn more about how domain reputation compares to IP reputation in our guide on how domain reputation affects email deliverability.
Older domains, even those with years of history, are not immune to reputation issues if their sending practices change or if historical issues were masked by the previous ESP's infrastructure. Mailbox providers are increasingly looking at recent sending behavior and engagement, rather than just the age of the domain.
Before migration (Mailchimp)
IP reputation: Mailchimp often uses shared IP addresses, benefiting from their collective positive sending history and volume, which can mask individual sender issues.
Domain reputation: Your domain builds its own reputation, but performance might be bolstered by the ESP's strong IP and infrastructure.
Bounce management: Mailchimp automatically handles bounces, including hard and soft, often removing problematic addresses without direct intervention.
After migration (new ESP)
IP reputation: You may be assigned a new dedicated IP or a different set of shared IPs, which lack prior sending history and need proper IP warming.
Domain reputation: Your domain's true reputation is exposed, as it's no longer shielded by the former ESP's robust infrastructure.
Bounce management: New ESPs might have different bounce handling, requiring you to actively monitor and clean your list.
Common pitfalls and their impact
One of the most critical factors impacting reputation after a migration is the quality of your mailing list. Sending to unengaged subscribers, or contacts who have not explicitly opted in for marketing emails, can rapidly lead to increased spam complaints and a damaged reputation. This includes users who signed up via Login via Gmail if they haven't explicitly consented to marketing communications.
Bounce management is another common pitfall. While hard bounces (permanent failures) are usually removed automatically by ESPs, soft bounces (temporary failures like account full) can also signal issues. Frequent soft bounces, even if temporary, can indicate a lack of engagement, or that the recipient's mailbox is poorly maintained, which can still negatively impact your sender reputation. Gmail has been particularly aggressive about this lately.
A lack of thorough root cause analysis for past deliverability issues from your previous ESP can also hinder recovery. If an account was closed down due to compliance problems, or if emails were sent from a domain without a proper MX record, these are strong negative signals that follow your sending domain. Without addressing these underlying issues, rebuilding reputation becomes significantly harder.
The hidden cost of uncleaned lists
Sending to unengaged or outdated email addresses, even those that only generate soft bounces, can severely damage your domain and IP reputation. These issues, often overlooked during ESP migration, lead to higher complaint rates and lower inbox placement rates. A bad IP reputation can directly impact your domain reputation.
Prioritize consent: Ensure all recipients have given explicit permission to receive your emails. Re-engagement campaigns are crucial for older lists.
Clean your list: Regularly remove inactive subscribers and addresses generating consistent bounces, whether hard or soft.
Monitor bounces: Understand the reasons for soft bounces, as some types can indicate deeper deliverability issues.
Strategic steps to rebuild sender reputation
Rebuilding sender reputation requires a disciplined and strategic approach. The first step is often a proper IP and domain warming plan, even for existing domains. This involves gradually increasing your sending volume over time, sending to your most engaged subscribers first. This signals to mailbox providers that you are a legitimate sender.
Meticulous list hygiene is non-negotiable. Beyond removing hard bounces, actively re-engage or suppress inactive subscribers. High engagement metrics, such as open rates and click-through rates, are strong positive signals, while low engagement, complaints, and bounces negatively impact your standing. Mailchimp itself recommends a reputation repair process focused on engagement and list cleaning.
Proper email authentication, including SPF, DKIM, and DMARC, is foundational. These records verify your sending identity and help mailbox providers trust your emails. Ensure they are correctly configured for your new ESP and consistently monitored. Incorrect or missing authentication can lead to immediate filtering or rejection of your emails.
Monitoring and adapting to new requirements
Continuous monitoring of your sender reputation is vital. Tools like Google Postmaster Tools provide invaluable insights into your domain and IP reputation, spam rates, and delivery errors. Regularly checking these dashboards can help you identify and address issues before they escalate.
Major mailbox providers, including Yahoo, are continually updating their algorithms and policies. What worked last year might not work today. Staying informed about these changes and adapting your sending practices accordingly is crucial for long-term deliverability success. This proactive approach helps avoid being placed on a blocklist (or blacklist).
Ultimately, rebuilding and maintaining a strong sender reputation after an ESP switch, especially from a platform like Mailchimp, requires commitment to best practices. This includes consistent, high-quality sending, meticulous list management, and robust email authentication. Focusing on these areas will lay the groundwork for reliable inbox placement.
Views from the trenches
Best practices
Maintain a clean and highly engaged email list by regularly removing inactive subscribers.
Implement a strict opt-in process, ensuring explicit consent for all marketing communications.
Gradually increase sending volume with a dedicated IP and domain warming plan tailored to your new ESP.
Ensure SPF, DKIM, and DMARC records are correctly configured and monitored for your sending domain.
Common pitfalls
Failing to conduct a thorough root cause analysis of past deliverability issues before migrating.
Sending to 'login via Google' users without explicit marketing consent, leading to complaints.
Ignoring soft bounces, especially 'account full' errors, as they can still indicate engagement issues.
Expecting instant reputation recovery without proper warming or list hygiene, leading to drops.
Expert tips
Continuously monitor your domain and IP reputation using tools like Google Postmaster Tools.
Adapt your sending strategy to evolving mailbox provider policies, as remediation times can increase.
Prioritize email authentication to build trust with receiving servers.
Focus on content quality and segmentation to improve subscriber engagement and reduce complaints.
Expert view
Expert from Email Geeks says that email deliverability has generally become more difficult since the changes introduced by Google and Yahoo, with content filtering becoming more nuanced and tighter.
2024-09-24 - Email Geeks
Expert view
Expert from Email Geeks says that Gmail remediation processes for deliverability issues are now slower than in the past.
2024-09-24 - Email Geeks
The path forward for a strong sending reputation
Rebuilding domain and IP reputation after migrating from an ESP like Mailchimp can indeed be a more arduous task today than it once was. This is largely due to the increasing sophistication of mailbox provider algorithms and their emphasis on transparent, consistent, and engaged sending practices.
The key to success lies in understanding that your domain's reputation is paramount and that past issues, even if previously masked, will surface. By prioritizing explicit consent, rigorous list hygiene, proper IP and domain warming, and robust email authentication, you can systematically rebuild trust with mailbox providers and achieve consistent deliverability for your emails.
Mailchimp often uses shared IP addresses, benefiting from their collective positive sending history and volume, which can mask individual sender issues.
Yahoo, are continually updating their algorithms and policies. What worked last year might not work today. Staying informed about these changes and adapting your sending practices accordingly is crucial for long-term deliverability success. This proactive approach helps avoid being placed on a blocklist (or blacklist).
