Well I thought so too.
The way I intended to use MailChimp for this scenario was:
1. All new users go in the Users list in mailchimp.
2. Under the Users list, I have multiple groups:
- Sent first message
- Liked a message
- Edited his profile
etc...
3. When a user does an action, I add him via the MailChimp API to the right group. (Can the same contact be in different groups?)
But then I stumbled upon this article: http://blog.mailchimp.com/autoresponder-triggers-in-mailchim...
"Some users have told us, “I don’t want to send autoresponders based on subscription to a list. I need to trigger them via the API to send to people already on my list.”
Our answer to that is NO."
I don't want my users to have to double opt-in again in MailChimp when they have already done it for my application.
Do I misunderstand how MailChimp works?