Passing checkbox values to Mailchimp
Mailchimp’s subscriber list stores more than just email addresses — you can add custom fields for names, cities, and other data. But when it comes to checkboxes, there’s no native checkbox field type in Mailchimp, which catches many developers off guard when they try to map a Contact Form 7 checkbox directly.
Problem: How do you pass checkbox values from Contact Form 7 (or any form) to Mailchimp?
Solution: Mailchimp doesn't support checkboxes natively. The two approaches are: use Mailchimp Groups to represent checkbox choices, or capture checkbox values via JavaScript, store them in hidden fields, and submit those to Mailchimp.
MailChimp organizes its subscriber data in a specific way: Fields hold information that identifies each subscriber (name, email, city, gender, etc.) — they do not support checkboxes. Groups are used to categorize subscribers by interest or preference, and this is where you can use checkboxes, radio buttons, or dropdowns — for example, "What topics would you like to hear about?" You can then create Segments based on fields, groups, or a combination of both, and send targeted emails to those segments.
NOTE: Mailchimp Groups (called Interest Categories in the API) can be managed programmatically via the Mailchimp API v3. If you’re using Contact Form 7 with the Mailchimp for WP plugin, interest group IDs can be mapped to form fields in the plugin settings without writing custom code.
Sources: