Is there a way to send an email to a mailchimp list on the event of a content type being published? The title says it all, really.

I want to trigger the dispatch of an email to a list of subscribers on mailchimp every time a certain content type is published.

Using rules I can see that the only mailchimp action available is to sign a user up to a list, so if there is a way of adding a new action to send an email to all users in a list that would be exactly what I need.

Any other methods are welcome too.

Thanks very much.
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!