Is there a way to send an email to a mailchimp list on the event of a content type being published?
I don't think you can do that directly from the interface. You need to create a hook function hook_rules_action_info in your custom module's .rules.inc file which will describe what the action actually does. See the link http://www.drupalcontrib.org/api/drupal/contributions!rules!rules.api.php/function/hook_rules_action_info/7
Even I'm looking for some good example or tutorial for this. Cheers!