I was creating a custom plugin which was to send certain emails based on the content/category of a post, but whilst trying to do that, I ran into some problems just getting a basic email sent out. Am I hooking on to the wrong function here? When I publish a post, nothing happens.

<?php
/**
* Plugin Name: Conditional Emailing
* Description: Sends emails based on categories.
* Version: 1.0
* Author: Ceds
*/

add_action( 'new_to_publish', 'conditional_email', 10, 0);

function conditional_email() {
  wp_mail('my@email.com','test','test');
}

?>

What am I doing wrong here?