How to modify Quick Mail sender permission

filter_quick_mail_sender_permission.php

<?php
/**
 * WordPress filter to modify the default Quick Mail sending permission.
 *
 * @param string $qm_user_capability
 * @return string new requirement
 * @link https://github.com/mitchelldmiller/quick-mail-wp-plugin
 */
function qm_sender_capability( $qm_user_capability )
{
	return 'list_users'; // administrator
}
add_filter( 'quick_mail_user_capability', 'qm_sender_capability' );