I looked carefully at MailChimp but I didnt see anything about being able to set up "Drip Campaigns" where people will get messaged using a predefined set of emails at given intervals after an event (such as a signup on a website). That's the secret sauce that I'm looking for - being able to add people to predefined workflows using an API and ideally push them down different paths, such as "Purchased" or "Didnt purchase after 60 days", so I can market to them more specifically and in an automatic way. This is what I meant by "Drip Campaign"
The magic word you're looking for in their documentation is Autoresponder. With the API, you just have some sort of state tracking field (I think they call them "Columns") and then segment the main list such that particular autoresponders go out to people who match a particular column value at N days past signup.
