Post offices (synonyms: postal services) are buildings where letters and packages can be sent and received. They may be located in towns or cities. In game-oriented worlds these may be places where players can send messages to one another or receive quests involving the delivery of a piece of mail. Historically, animals such as carrier pigeons have been used to relay messages between locations. In fictional worlds consider ravens, owls, sprites, mini-dragons, robots, and other creatures as postal workers. Post offices may have extensive conveyor systems in their back rooms to help sort the mail.