When a Mail-Gateway object is created in the directory, Microsoft Exchange Server creates a special mailbox in the server’s information store for the gateway. This mailbox includes two folders, MTS-IN and MTS-OUT, which are used as message queues. The server places mail addressed to the foreign system in the MTS-OUT folder, and the gateway service places messages from the foreign system in the MTS-IN folder. The gateway uses MAPI functions and methods to access these folders.