Debug wp_mail function. Display errors on screen

debug-wpmail.php

<?php
/**
 * Display errors
 */
if ( ! function_exists('debug_wpmail') ) :

	function debug_wpmail( $result = false ) {

		if ( $result )
			return;

		global $ts_mail_errors, $phpmailer;

		if ( ! isset($ts_mail_errors) )
			$ts_mail_errors = array();

		if ( isset($phpmailer) )
			$ts_mail_errors[] = $phpmailer->ErrorInfo;

		print_r('<pre>');
		print_r($ts_mail_errors);
		print_r('</pre>');
	}
endif;


/**
 * Usage
 */
$res = wp_mail($to, $subject, $message);
debug_wpmail($res); // Will print_r array of errors