Migrate Existing Subscribers (and Unsubscribes) into Klaviyo

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There are several ways to load existing subscriber lists into Klaviyo, which we will walk through in the following sections. You will learn best practices around getting started with Klaviyo as well as how to add existing lists into your account. 

If you are interested in redirecting existing signup forms to Klaviyo instead of migrating an existing list of subscribers, head to our article on redirecting these forms instead.

Before Jumping In

To start, we recommend that you maintain one main list in your account, such as a Newsletter. As you import contacts and connect signup forms to Klaviyo, maintaining one primary list will make it easy to manage and communicate with your contacts efficiently.

Our segment builder allows you to create dynamic subsets of your lists that don’t require any maintenance. For example, instead of having different signup forms on your site link to different lists, have all forms point to one list. Then, pass a sign-up source property ($source) that is unique for each form. This way, you maintain one subscriber list and create segments based on this property.

Sync Contacts from Another Email Service Provider (ESP)

If you are migrating from Mailchimp, Campaign Monitor, Constant Contact, MadMimi, or ExactTarget you'll use a built-in integration with Klaviyo to import existing subscriber lists, as well as unsubscribes. To do this, you will want to configure the relevant integration.

Navigate to your Integrations All Integrations, and filter the Category to Email. Here, you'll see all of our current built-in ESP integrations.

Once your integration is added, your lists will automatically sync and appear in your account's Lists & Segments tab within a few minutes.

All unsubscribed contacts will also sync and go straight to the suppression list in your account.

  • For MailChimp, Campaign Monitor, and MadMimi we create an exclusion list automatically for those that are unsubscribed. In MailChimp, if someone is suppressed in any list, they will be globally suppressed in Klaviyo.
  • For Contact Contact, we only sync a suppression list if they belong to a Constant Contact List ID of 'do-not-mail.’

If you are not currently using an ESP we integrate with, you will need to take a more manual approach (outlined in the next section).

Import Contacts from a CSV File

If you are using an ESP that we do not currently integrate with or have a subscriber list already saved as a CSV or Excel file, you can easily import or copy and paste your subscribers into Klaviyo. If you have your list as an Excel file, make sure to save it as a CSV file first.

Your CSV should have the first row formatted as the headings for the columns you intend to upload. You must have a column labeled "Email" or "Email Address." Other columns you may want to include are "First Name" and "Last Name," along with any other custom properties you wish to upload.

When importing a list from another ESP, most platforms have a link to export lists to a CSV or Excel file. If you're having trouble, we recommend reaching out to your current platform for help.

Once you have your list exported, navigate to the Lists & Segments tab in Klaviyo and click on the list called Newsletter. Within this list, if it's empty, choose the Upload Contacts option to import your CSV file.


If you already have subscribers in this list, click Manage List in the upper right and you'll see these same options for how you can add additional contacts to your list.

Then, you will be able to drag and drop your CSV directly into Klaviyo or select it from your files. Alternatively, you can select Upload via copy/paste instead, and copy and paste your list into Klaviyo.


You will be taken to a page where you can review the data you are importing. Select Import Review.


You will then be able to preview how many columns and new properties will exist in your import. If this information is correct and you are ready to complete this process, select Start Import.


Use the Klaviyo API

The Lists & List Management API is used to create and manage lists in Klaviyo. If you're tech-savvy or have a developer, you can use Klaviyo's List API to import existing subscribers.

Load Historic Unsubscribes into Klaviyo

If you did not sync subscribers through one of our built-in ESP integrations, you will want to manually import your historic list of bounces and unsubscribes into Klaviyo.

This step is important for several reasons:

  • To make sure you follow spam laws
  • To keep your email deliverability high by sending to clean lists off the bat
  • To keep your subscribers happy and make sure you don't email anyone who has opted out

The first step is preparing a CSV file of bounces and unsubscribes. Once you have this file ready, navigate to the Profiles tab in Klaviyo and click Suppressed Profiles in the upper right.


Click Suppressed Profiles to arrive at your account's suppression list.

Here, you will see three options: Export CSV, + Add Email Address, and Upload File.

Select Upload File to import your list of bounces and unsubscribes. Note that your file should be formatted as a CSV with a single column or as a text file with one email per line. There is no need to add a title to your one column for emails or add any additional columns.

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