Send marketing campaigns and transactional mails.
Mailchimp API is a free Business API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Find all the Mailchimp API documentation and tools developers need to send marketing and transactional emails.
Details from mailchimp.com.

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The Mailchimp API is provided by Mailchimp (mailchimp.com). Find all the Mailchimp API documentation and tools developers need to send marketing and transactional emails.
Yes. The Mailchimp API is listed in the Business category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Mailchimp API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Mailchimp API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Mailchimp API is served over HTTPS, so it's safe to use in production.