Mail - attachments is unlocked at level 400 with 125k influence. You can receive attachments before this. Limited items can be sent: Demon Horns, Voidshards, Siege guns, Rare mob drops (judge tokens, Griswold Crates), Crates of bottles, Rune Chests (small, medium and special), Equipment Chests, Ammunition boxes, Armies (Dark Knight and Human), Anarijel (hero if still in box), Nut and Fiery Eye (found mainly with random item crafts and crafted).(edited)