This paper reports the design and implementation experience of a network mail message system which permits communication between different computer systems. The authors describe the message gateway being implemented. They also describe the “envelope” file facility, which is separate from the message contents and is used to provide a uniform treatment of messages passing through the gateway. The implementation status at the time of this report seems to be in its first phase. Nevertheless, the authors’ experience may be a valuable guideline for designers of a network mail system dealing with a diversity of heterogeneous message systems and networks. The authors discuss a number of interesting future development ideas, such as a network-wide user directory service. Interested readers deserve further inquiry into the current implementation status of such ideas.