[Plugin: Notify on comment] Getting a string of authors’ emails

I am using Co Authors Plus to give me more than one author for a post and also Notify on comments to let the Author know when a post has been commented on (not sure why this isn’t part of the core).

The problem is that the code for notify on comments uses

$user = get_userdata($post->post_author);
	$to = $user->user_email;

which only gets the email for the Primary author. There are all sorts of great tags from Co-Authors Plus which I know will return the info that I need, but I have no idea how to get these two lines to work when there is more than one email address.

If anyone can help me I would be enormously grateful.