Mailchimp Integration

Subscribe an email address to a Mailchimp list when a form is submitted. Requires the MC4WP (Mailchimp for WordPress) plugin.

Action type: mailchimp Class: Core_Forms\Actions\MailChimp Source: src/actions/class-mailchimp.php

Prerequisites

This integration requires the MC4WP - Mailchimp for WordPress plugin to be installed and connected to your Mailchimp account.

1. Install and activate the MC4WP plugin.
2. Go to MC4WP > Mailchimp and connect your Mailchimp API key.
3. Ensure your lists are synced.

Setup

1. In WordPress, edit your form > Actions tab > Add Action > Mailchimp.
2. Select the Mailchimp list from the dropdown.

If no lists appear, click the link to connect your Mailchimp account in the MC4WP settings first.

Settings Reference

Setting	Required	Default	Description
List	Yes	--	Mailchimp audience/list to subscribe to (dropdown from MC4WP)

Email Detection

The integration automatically finds the email address in the submission data. It scans all submitted fields and uses the first value that passes is_email() validation. No explicit email field mapping is needed.

Subscriber Status

New subscribers are added with pending status, meaning they will receive a double opt-in confirmation email from Mailchimp before being fully subscribed.

Merge Fields

Custom merge fields can be added via the cf_mailchimp_action_merge_fields filter:

add_filter( 'cf_mailchimp_action_merge_fields', function( $merge_fields, $submission, $form ) {
    $merge_fields['FNAME'] = $submission->data['first_name'] ?? '';
    $merge_fields['LNAME'] = $submission->data['last_name'] ?? '';
    return $merge_fields;
}, 10, 3 );

Subscriber Data

The full subscriber data array can be modified via the cf_mailchimp_action_subscriber_data filter:

add_filter( 'cf_mailchimp_action_subscriber_data', function( $data, $submission, $form ) {
    $data['status'] = 'subscribed'; // Skip double opt-in
    $data['tags']   = [ 'website-lead' ];
    return $data;
}, 10, 3 );

Error Logging

Errors are logged via the MC4WP debug log (mc4wp_get_debug_log()):

• Already subscribed (error code 214): logged as a warning
• Other API errors: logged as errors
• Successful subscriptions: logged as info

View logs at MC4WP > Other > Debug Log.

How It Works

1. Scans all submitted fields for a valid email address.
2. If no email is found, the action silently returns.
3. Applies the cf_mailchimp_action_merge_fields filter for custom merge fields.
4. Applies the cf_mailchimp_action_subscriber_data filter for full data control.
5. Calls MC4WP_MailChimp::list_subscribe() with the list ID, email, and data.
6. Logs the result to the MC4WP debug log.

Troubleshooting

• "Please connect your Mailchimp account first": Install and configure the MC4WP plugin before using this action.
• No lists in dropdown: Go to MC4WP settings and refresh the list cache.
• Subscriber not appearing: Check if double opt-in is enabled (default). The subscriber must confirm via email.
• Already subscribed: This is logged as a warning, not an error. The subscriber already exists on the list.