This hook is run after successfully passing error validation. This hook only fires if the send confirmation email to the requester is set to yes in the settings.

function my_custom_function($confirm_email, $subject, $message) {
	$confirm_email; // Email from the reserve form (reserving party email)
	$subject; // Subject of the email that was sent out
	$message; // Message of email sent

	// Do whatever you want with this information


add_action('reserve_confirmation', 'my_custom_function', 10, 3);