inc/class-Iac_Threaded_Mails.php
public static function get_instance() {

		if ( ! self::$instance instanceof self ) {
			$new = new self;
			$new->init();
			self::$instance = $new;
		}

		return self::$instance;
	}
public static function get_instance() {

		if ( ! self::$instance instanceof self ) {
			$new = new self;
			$new->init();
			self::$instance = $new;
		}

		return self::$instance;
	}
get the instance

@return Iac_Threaded_Mails