MailChimp, an email marketing tool used by the likes of Firefox and Media Temple, recently announced the addition of web hooks to their API. Their primary use-case is to keep your email list in sync with theirs. They push to your callback URL with several types of events regarding list changes, including subscribes, unsubscribes, profile updates, cleaned addresses, and email changes.
Their API documention explains web hooks and how you use them with MailChimp. They also mention PostBin as an excellent utility to help see the event data as they’re triggered in their system.
