Concerning the Priority Mail, you need to do the sidequest twice to get both items. One is if you bring it to Kafei's Mother, yourself or if you let the postman deliver it to her. If you bring it to her while wearing Kafei's Mask, she'll give you a new bottle filled with Chateau Romani. You can also enter the Bar before it opens at 7pm if you don't have Romani's Mask, which is proof of membership.