The infrastructure described in this chapter uses the client/server model to provide a public mail service through the telephone line. In this configuration, we (the poeple building the infrastructure) provide the information you (the person using the infrastructure) need to know in order to establish a point-to-point connection from the client computer to the server computer through the telephone line. The infrastructure described in this chapter is made available to you free of charge, however, you should know that maintaining it costs both money and time. For example, for each hour the server computer is on production there is an electrical consume that need to be paid every month. Likewise, each call that you establish from the client computer to the server computer will cost you money, based on the location you made the call from and the time you spend connected. In this chapter we discuss usage convenctions we all must be agree with, in order to achieve a practical and secure interchange system.