milanIntermaps

Can someone exmplain me how that substitution_tag works? ``` $email = new Mail(); $email->setClickTracking(true, true); $email->setOpenTracking(true, "--sub--"); $email->setSubscriptionTracking( true, "subscribe", "subscribe", "%%sub%%" ); $email->setSubject("Sending with Twilio SendGrid is Fun 2");...