MailChimp Destination

Mailchimp provides email marketing automation for e-commerce businesses. With Segment you can add people to your MailChimp list with a single identify call.

This document was last updated on May 08, 2018. If you notice any gaps, out-dated information or simply want to leave some feedback to help us improve our documentation, please let us know!

Use Cases

Getting Started

The first step is to make sure MailChimp supports the source type and connection mode you’ve chosen to implement. You can learn more about what dictates the connection modes we support here.

📱 Device-based
☁️ Cloud-based
  1. From your Segment UI’s Destinations page click on “Add Destination”.
  2. Search for “MailChimp” within the Destinations Catalog and confirm the Source you’d like to connect to.
  3. Drop in your MailChimp “API key” into the connection settings. It is recommended that you create a brand new API key for the Segment destination. MailChimp restricts each API key to a maximum of 10 concurrent requests, so creating a dedicated one for Segment will ensure maximum throughput for outgoing calls. You can read more about API keys on MailChimp’s docs.
  4. Drop in your MailChimp “Audience ID” into your connection settings.


If you haven’t had a chance to review our spec, please take a look to understand what the Identify method does. An example call would look like:

analytics.identify('userId12345', {
  firstName: 'Bob',
  lastName: 'Dole',
  email: ''

Every time you call identify with an email address included, we will:

  1. First ask Mailchimp if that email exists and what their subscriber status is for the listId you have provided in the destination settings.

  2. If they do not exist, we will subscribe that user to the list immediately. If you have doubleOptIn setting enabled, it will send a confirmation email to that user before subscribing them and that email will not be tagged with a subscriber status of pending.

  3. If they already have a subscriber status such as pending, subscribed, unsubscribed or cleaned, we will NOT resubscribe them but simply update their user traits.

So you no longer have to worry about the identify call resubscribing users unintentionally!

Segment recognizes firstName, lastName and email as special traits, so we will translate those for you to match the Mailchimp accepted field names. Mailchimp includes these fields by default when you create a list.

Recording Custom User Traits

If you want to view any other custom user traits in the Mailchimp list dashboard, you must create a Custom Merge Field inside Mailchimp’s UI of the traits in your identify calls. Note that you do not need to map all user.traits you are sending inside Mailchimp. You only need to create Custom Merge Fields of the traits you want to see in your list view.

IMPORTANT: Mailchimp only supports merge tags that are 10 characters or shorter. So for every user trait you send inside the .identify() call, we will trim it to be the first 10 characters and will send it in uppercase form to Mailchimp. So it’s very important that when you set up your merge tags in Mailchimp, your Merge Tags are the first 10 characters (excluding whitespace or special characters) of its Field Label (if it’s over 10 characters).

For example, if your Field Label was Way Too-Long123, your Merge Tag should be WAYTOOLONG. And the user.trait inside your .identify() call would be Way Too-Long123 since we will convert that to WAYTOOLONG before sending it to Mailchimp.

If you are going to be sending either a boolean or null object as a user.trait value, when creating the custom merge field for that trait inside Mailchimp, make sure to set the data type as TEXT since we will stringify all boolean or null objects to strings.

Also note that fields you specify in Mailchimp as date fields must receive dates. Passing non-date values will cause issues.

Custom Merge Fields

To send custom merge fields/user traits to Mailchimp you need to create the merge field first in Mailchimp for each trait you want sent to Mailchimp. Then when you call identify with keys that match those traits they will appear in your Mailchimp list.

For example, if you have a list in Mailchimp with these custom merge fields:

mailchimp merge fields screenshot

You can populate those fields using this identify call:

analytics.identify('userId12345', {
  firstName: 'Bob',
  lastName: 'Dole',
  email: '',
  company: 'Initech',
  employees: 234

For any other custom traits just add a Mailchimp Custom Merge Field inside of Mailchimp with a tag that matches the key you are using in your identify call. In the example these traits are company and employees. They will be shown as COMPANY and EMPLOYEES in Mailchimp, but you can record them in lower-case to identify and they will still be populated.

One thing to note is that you shouldn’t use underscores in your custom Merge Field names.

Once Mailchimp has processed the new subscriber you’ll see it show up in your list, like this:

mailchimp subscriber screenshot

Recording userId

If you send a userId in your .identify() call, we will attach it as Mailchimp’s semantic unique_email_id for that user. This is a read-only unique identifier for that email across all of Mailchimp.

Overriding List ID (Also now referred to as Audience ID)

If you have multiple lists (audiences) that your users can subscribe to, you can override the default list (audience) ID. Simply send a listId parameter as an option for Mailchimp:

analytics.identify('userId12345', {
  firstName: 'Bob'
  }, {
    "MailChimp": {
      "listId": "ea7918abb6"

Manually updating user subscription status

If you’d like to manually update a user’s subscription status, you can do so by passing in subscriptionStatus property as an option for Mailchimp:

analytics.identify('userId12345', {
  firstName: 'Bob'
  }, {
  integrations: {
    "MailChimp": {
      "listId": "ea7918abb6",
      "subscriptionStatus": "unsubscribed"

Important: You must use the semantic property exactly as is, subscriptionStatus (case-sensitive) and the value of this property must be one of the four valid statuses supported by Mailchimp: pending, subscribed, unsubscribed, and cleaned (all lowercase).

Again, this will NOT work for new users. New users will always have their subscription status set as either pending or subscribed depending on your double opt-in setting.


Why are my calls with trait arrays not showing up in MailChimp?

MailChimp does not support arrays as traits values. This can cause calls to not show up.


You can send computed traits and audiences generated through Segment Personas to this destination as a user property. To learn more about Personas, reach out for a demo.

For user-property destinations, an identify call will be sent to the destination for each user being added and removed. The property name will be the snake_cased version of the audience name you provide with a true/false value. For example, when a user first completes an order in the last 30 days, we will send an identify call with the property order_completed_last_30days: true, and when this user no longer satisfies we will set that value to false.

When the audience is first created an identify call is sent for every user in the audience. Subsequent syncs will only send updates for those users which were added or removed since the last sync.


Segment lets you change these destination settings via your Segment dashboard without having to touch any code.


You create and copy-paste your MailChimp API Key from Account Settings > Extras > API Keys.

Datacenter ID

You can find your Datacenter ID in the MailChimp url in your browser when you’re logged in. It’s the ‘us1’ in ‘‘.

Double Opt-In

An optional flag to control whether a double opt-in confirmation message is sent when subscribing new users.

Audience ID

You can find your Audience ID in your Mailchimp Settings pane under the Audiences tab. Go to Manage Audiences > Settings and click on Audience Name & Defaults. The Audience ID will be on the right side.

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