Only use Mandrill for one plugin

Of course the obvious answer is don’t use the plugin – use the API in my plugin.

Using the Mandrill plugin exposes some nice metrics on the WordPress dashboard, but we only want to use Mandrill for a limited set of our outbound WP email.

Other recommendations?

I could have this solution wrong, and I’m going to assume you have a bit of wordpress development experience.

To force WP to use the native wp_mail() function, you could use this:

function force_native_wp_mail( $message ) {
   $message['force_native'] = 1;
   return $message;
}
add_filter( 'wp_mail', 'force_native_wp_mail' );

How you then use that filter as and when you need it, is up to you.
Hope that helps.
Paul.