Klaviyo Mailchimp Integration: Sync, Run Both, Cut Over

Yes, Klaviyo has a built-in Mailchimp integration, but it only syncs one way: contacts, audiences, subscription status, suppressions and the last 90 days of campaign engagement move into Klaviyo, and nothing flows back to Mailchimp. Tags, templates, campaigns and automations don’t move at all.

That makes it a migration tool. If you’re moving off Mailchimp for good, it handles the list and consent, and our Mailchimp to Klaviyo migration covers the rest of the move. If you’re still deciding between the two, start with Klaviyo vs Mailchimp. If you want to run both for a while, the integration barely helps, and that gap is where problems start.

This guide covers exactly what the integration moves, how to run both platforms safely, and the cutover plan we use so customers never get two abandoned cart emails.

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What the Klaviyo Mailchimp integration does

Klaviyo’s Mailchimp integration is a one-way import. You connect it with a Mailchimp API key, and it pulls your audiences into Klaviyo as lists, with subscription status, suppressions and 90 days of campaign engagement. Nothing syncs back to Mailchimp, and tags, templates and automations don’t come across. It’s a migration tool.

Here is what moves, per Klaviyo’s Mailchimp migration guide (updated 30 March 2026, checked 10 October 2026):

Data	Syncs?	Notes
Contacts (email, name, location)	Yes	Mailchimp audiences become Klaviyo lists
Subscription status	Yes	Unsubscribed contacts stay unsubscribed
Cleaned and bounced contacts	Yes	Added to Klaviyo’s suppression list, with one exception (below)
Campaign engagement	Yes	Opens, clicks and receives from sent campaigns in the last 90 days, excluding A/B tests
Mailchimp contact ratings	Yes	Only if you let it create Klaviyo lists from your audiences
Tags	No	Export per tag, import as a Klaviyo profile property
Templates	No	Export the HTML, swap merge tags, import to Klaviyo
Automations	No	Rebuild as Klaviyo flows
Contacts deleted in Mailchimp later	No	They stay in Klaviyo
Anything from Klaviyo back to Mailchimp	No	The integration is one-way

Sync timing. The first sync pulls all contacts and the last 90 days of campaign data. After that, existing audiences sync every 30 minutes, and new audiences or campaigns every six hours.

The suppression exception. If a profile already exists as active in Klaviyo before you connect Mailchimp (because your Shopify integration created it, for example), a “cleaned” status in Mailchimp won’t suppress it. Klaviyo’s fix is to export cleaned contacts from Mailchimp as a CSV and upload them to your Klaviyo suppression list manually. Skip this and you’ll re-mail addresses Mailchimp already knew were dead, which is the fastest way to start a new platform with a bounce problem. Our Klaviyo bounced emails guide covers why that matters.

How to connect it

1. Disconnect Mailchimp from Shopify first, if Shopify is already connected to Klaviyo. Klaviyo’s guide warns that skipping this can send double opt-in emails to your existing list.
2. Generate an API key in your Mailchimp account settings.
3. In Klaviyo, go to Integrations, find Mailchimp, and paste the key.
4. Choose the advanced options: whether to sync open and click data, whether to create Klaviyo lists from Mailchimp audiences, and (with list creation on) which audiences to sync.
5. Check the data within a few minutes: list counts, a sample of unsubscribed profiles, and the suppression list.

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Running Mailchimp and Klaviyo at the same time

There are legitimate reasons to run both. The most common is a cutover window of two to six weeks while flows are rebuilt. Less often, a business keeps Mailchimp for a separate newsletter or a service arm and uses Klaviyo for the store.

The built-in integration isn’t designed for either case, because it only moves data one way. Three problems show up if you rely on it:

• Unsubscribes don’t travel back. Someone who unsubscribes from a Klaviyo email is still subscribed in Mailchimp. Under the US CAN-SPAM Act, per the FTC, you must honour opt-outs within 10 business days, and UK, EU, Australian and Canadian rules are stricter on consent. An opt-out has to reach every platform that can mail that person.
• Double sends. If a Mailchimp abandoned cart automation and a Klaviyo abandoned cart flow are both live, customers get both. We still find this in accounts months after a “completed” migration.
• Split reporting. Revenue attribution lives in two places with two different models, and neither sees the whole customer.

How to sync lists both ways

If you genuinely need both platforms live beyond a short cutover, add a two-way layer on top of the native integration:

• Zapier (or Make) has triggers and actions for both apps. The essential Zap is Mailchimp New Unsubscriber → Klaviyo Unsubscribe Profile, plus the reverse direction. New subscriber sync can run the same way.
• One owner per job. Decide which platform sends what. Klaviyo owns every store-triggered flow. Mailchimp, if it stays, owns only the thing Klaviyo doesn’t do for you, and its automations for carts, welcome and post-purchase get switched off.
• One source of truth for consent. Pick the platform where sign-up forms live and treat the other as a follower.

If you can’t name a reason Mailchimp needs to stay after the cutover, it shouldn’t. Two platforms cost more in subscriptions, in attention and in mistakes than they return.

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The cutover plan

This is the order we run it in. Each step exists because skipping it causes a specific, avoidable failure.

Week	Step	What it prevents
0	Connect your store to Klaviyo and let the history sync	Flows launching against empty profiles
0	Set up a branded sending domain with SPF, DKIM and DMARC in Klaviyo	Your first sends landing in spam
0	Disconnect Mailchimp from Shopify, then connect the Mailchimp integration	Double opt-in emails to your whole list
1	Export Mailchimp tags and import them as profile properties	Losing segments you built over years
1	Upload cleaned contacts to Klaviyo’s suppression list	Re-mailing dead addresses
1–3	Rebuild automations as Klaviyo flows, starting with welcome, abandoned cart, browse and post-purchase	Revenue gaps when Mailchimp goes quiet
2–3	Send campaigns from Klaviyo to your most engaged segment first, then widen	Reputation damage on a new sending setup
3	Switch every sign-up form to Klaviyo	New subscribers landing in the old platform
3	Same day: pause Mailchimp automations, turn Klaviyo flows live	Two cart emails, or none
4	Verify counts and consent, then remove the integration	Stale syncs overwriting clean data

Four details that decide whether it goes smoothly

1. Warm up by engagement. Start with people who opened or clicked in the last 30 days and widen over two to three weeks. Klaviyo’s own migration guides recommend this staged approach. A new sending setup has no history, and mailbox providers judge it on early engagement.
2. Rebuild flows, don’t copy them. A straight port of Mailchimp automations into Klaviyo wastes the reason you switched. Klaviyo triggers on Started Checkout, Viewed Product and predicted next-order date, which Mailchimp can’t. Our flow automation work starts from those triggers.
3. Check your billable profiles. Klaviyo bills on active profiles. Importing a list full of long-dead contacts inflates the invoice from day one, so the migration is the right moment to clean the list. Suppressed profiles don’t count toward billing.
4. Keep Mailchimp exports. Before closing the account, export campaign reports and any audience data you might need later. Once the integration is removed and the account closed, that history is gone.

Mailchimp also documents the reverse move, a Klaviyo to Mailchimp migration, so the same care applies in either direction.

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Is Klaviyo or Mailchimp better?

For a store with meaningful order volume, Klaviyo, because the data it acts on is deeper: full order and product events, predictive properties, and flows triggered by behaviour rather than list membership. For a newsletter-led business with little store data, Mailchimp is a perfectly reasonable tool, and it’s cheaper to run well. We lay out the full comparison, including when to stay, in Klaviyo vs Mailchimp.

Is there an API for Mailchimp?

Yes. Mailchimp’s Marketing API is what Klaviyo’s integration uses, which is why setup starts with generating a Mailchimp API key. The same API powers Zapier and custom syncs if you need data to move in both directions.

Why is Klaviyo more expensive than Mailchimp?

Often it isn’t at small list sizes, and when it is, the difference is usually the depth of automation you’re paying for. Klaviyo prices on active profiles, so list hygiene has a direct effect on the bill. Our Klaviyo pricing breakdown covers the maths.

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Moving off Mailchimp without losing anything

The integration does the easy part: moving contacts and consent. The part that decides whether the switch pays off is the cutover order, the suppression clean-up and flows rebuilt around Klaviyo’s triggers. That’s what our Mailchimp to Klaviyo migration covers end to end. If you’d like a view on your account first, start with a free Klaviyo audit. We’ll tell you what should move, what shouldn’t, and whether running both makes sense for you at all.