Mail Order Mystery Once A Year Coupon: Save $5 on any Mystery! Posted by Hello Subscription on October 10, 2017. Subscription Box Coupons & Deals Make the first comment! Hello Subscription independently researches and reviews the best subscriptions and products. Things you buy through our links may earn us a commission. Save for LaterGo to commentsNotification Mail Order Mystery is offering the only coupon code it will have all year! Just enter the code EARLYBIRD at checkout to save $5 on any mystery. Valid until Sunday.