How to warm up a small email list when migrating from Mailchimp to Klaviyo?
Matthew Whittaker
Co-founder & CTO, Suped
Published 18 May 2025
Updated 17 Aug 2025
6 min read
Migrating your email list from one platform to another, especially from Mailchimp to Klaviyo, requires careful consideration of email warming. Even with a seemingly small list, like 12,000 subscribers, proper warming is essential to protect your sender reputation and ensure your emails reach the inbox. Many assume that a smaller list size reduces the need for warming, but this isn't necessarily true, particularly when switching email service providers.
The goal is to gradually introduce your sending activity on the new platform to internet service providers (ISPs). This builds trust and signals that you are a legitimate sender. Rushing the process, even with a smaller list, can lead to your emails being flagged as spam, ending up in junk folders, or even getting your domain added to a blocklist (or blacklist).
Understanding warming for small lists
Even with a list of 12,000 subscribers, warming is still a critical step. While it's not the same as warming a list of 100,000, you still need to establish your sending patterns with ISPs from the new platform. Your domain has an existing reputation from Mailchimp, but the sending infrastructure on Klaviyo is new for your domain. ISPs need to see consistent, positive engagement from this new source.
Klaviyo generally uses shared IP addresses for most accounts. Even if you're using a dedicated sending domain, the underlying IP addresses are shared among many users. This means the reputation of those IPs is influenced by everyone sending through them. Your domain reputation, however, is distinct. You need to warm up your domain's sending behavior on these shared IPs, especially for a small list.
While Klaviyo offers a Guided Warming feature, it primarily tracks sending activity and engagement within Klaviyo itself. If you're still sending emails from Mailchimp during the migration phase, Klaviyo's warming metrics won't account for opens or clicks happening on the old platform. This can give you a skewed view of your true engagement and lead to warnings that might seem concerning but aren't necessarily reflective of your overall list health.
Pre-migration checklist and data cleanup
Before you even begin sending from Klaviyo, the most crucial step is to clean your email list. Migrating a dirty list, even a small one, can severely damage your sender reputation. Remove inactive subscribers, bounces, and potential spam traps. Engage those subscribers who haven't opened emails in a long time before transferring them.
Clean list (Before migration)
High engagement: Focus on subscribers who have recently opened or clicked emails.
Faster warming: ISPs see positive interactions quickly, accelerating trust.
Unclean list (After migration)
Low engagement: Sending to unengaged contacts can lead to low open rates.
Increased risk: Higher bounce rates and spam complaints can harm your sender reputation.
Slower warming: ISPs may delay or filter your emails, prolonging the warming process.
Equally important is the proper setup of your DNS records for email authentication. This includes SPF, DKIM, and DMARC. Your domain's sender authentication should be fully configured and validated within Klaviyo before you send your first campaign. If you plan to send from a dedicated sending domain, you must configure that within Klaviyo. Until your DNS records are correctly in place for Klaviyo, it's better to continue sending from Mailchimp.
Importance of DKIM
Do not start your warming process until you have DKIM authentication in place. DKIM helps verify that your emails are legitimately from your domain and haven't been tampered with in transit. This is a fundamental step for establishing trust with ISPs, regardless of your list size. You can read more about improving Klaviyo deliverability through proper setup.
Crafting your warming schedule
Even with 12,000 subscribers, a slower, more deliberate warming schedule is advisable. While Klaviyo's recommended warming volumes might suggest you can finish in a week or so, extending it over two to four weeks (or even longer, depending on your engagement) is safer. This gives ISPs more time to recognize your sending patterns and build a positive reputation for your domain on the new platform. For more nuanced advice, consider warming up a new client's list.
A good strategy involves segmenting your list based on engagement. Start by sending to your most active subscribers first, then gradually expand to less engaged segments. This sends positive signals to ISPs. If you typically send three times a week, maintain that frequency during warming. For example, if your most engaged segment is 2,000 people, send to them initially, then increase the segment size incrementally for subsequent sends.
Here's a sample progression, assuming you've segmented your 12,000 subscriber list by engagement:
Week
Daily Send Volume (Klaviyo)
Cumulative Send Volume (Klaviyo)
Notes
Week 1
2,000
6,000 (3 sends)
Target most engaged subscribers (e.g., opened in last 30-60 days). Maintain normal sending frequency.
Week 2
4,000
12,000 (3 sends)
Expand to include subscribers engaged in last 60-90 days. Monitor metrics closely.
Week 3
6,000-8,000
18,000-24,000
Continue increasing volume, including less recent openers. Ensure stable engagement.
Week 4+
Full list (up to 12,000)
As needed
If metrics are stable, gradually introduce the entire list. Consider segmenting by engagement level.
Monitoring reputation and adapting your plan
During your warming period, consistent monitoring of your sender reputation and deliverability metrics is non-negotiable. Pay close attention to your open rates, click-through rates, bounce rates, and spam complaint rates. Tools like Google Postmaster Tools are invaluable for this, providing insight into your sending reputation with Gmail and other key metrics. If you see any dips in engagement or increases in complaints, slow down your sending volume immediately.
When using Klaviyo's Guided Warming and still sending some emails through Mailchimp, remember that Klaviyo's warnings are likely based only on the data it collects directly. This means if subscribers are opening emails sent from Mailchimp, Klaviyo won't factor that into its warming guidance. In such cases, if you're pulling combined open data into your segmentation, you can often proceed cautiously, but always prioritize actual inbox placement and engagement metrics over platform-specific warnings.
Being listed on an email blocklist (or blacklist) can severely impact your deliverability. Regularly check if your domain or IP is listed on any major blocklists. If you find your domain listed, you'll need to address the underlying issues, such as high bounce rates or spam complaints, and then request de-listing.
Views from the trenches
Best practices
Always clean your email list thoroughly before migrating to a new ESP, regardless of list size.
Prioritize setting up and verifying all email authentication records (SPF, DKIM, DMARC) on your new platform.
Segment your list by engagement and start sending to your most active subscribers first to build positive reputation.
Monitor your deliverability metrics closely using tools like Google Postmaster Tools.
Common pitfalls
Rushing the warming process by sending too much too soon can lead to emails landing in spam folders.
Ignoring list hygiene and importing unengaged contacts or spam traps from your old platform.
Failing to properly configure email authentication (DKIM, SPF, DMARC) before starting sends on the new ESP.
Relying solely on the new ESP's internal warming metrics, especially if still sending from an old platform.
Expert tips
Even for small lists, a gradual introduction of sending volume helps ISPs build trust in your domain on new infrastructure.
If sending from a dedicated domain on shared IPs, focus on domain reputation, which is influenced by your sending behavior.
If you need to send from the old ESP as a bridge, segment your sends to avoid overlapping recipients and confusion.
Pay close attention to user engagement signals as these are crucial for establishing a good sender reputation.
Marketer view
A marketer from Email Geeks says that if you send emails daily, you could reach your warming plan goal quickly, but spreading it out over a few weeks and monitoring deliverability rates with Google's tools is a better approach.
2023-07-06 - Email Geeks
Expert view
An expert from Email Geeks emphasizes that you should not start warming until DKIM authentication is fully in place, as it's a critical step for improving deliverability.
2023-07-06 - Email Geeks
Summary
Migrating a small email list from Mailchimp to Klaviyo requires a strategic approach to warming, even with a smaller list size. The key is to prioritize list hygiene, ensure all email authentication records are correctly set up, and implement a gradual sending schedule that builds trust with ISPs.
By patiently executing a well-planned warming strategy and diligently monitoring your deliverability metrics, you can successfully transition your email program to Klaviyo while maintaining a strong sender reputation and ensuring your valuable emails reach the inbox.
Mailchimp to 
Klaviyo, requires careful consideration of email warming. Even with a seemingly small list, like 12,000 subscribers, proper warming is essential to protect your sender reputation and ensure your emails reach the inbox. Many assume that a smaller list size reduces the need for warming, but this isn't necessarily true, particularly when switching email service providers.
Gmail and other key metrics. If you see any dips in engagement or increases in complaints, slow down your sending volume immediately.
