Gateways that need to interoperate properly with the Microsoft Exchange Server Internet Mail Service need to take some precautions with their use of TNEF encoding. Any gateway that delivers messages to the Internet at large should do this because it is not possible to know whether a recipient on the Internet will receive the message via Microsoft Exchange Server. This section describes how the Microsoft Exchange Server Internet Mail Service uses TNEF so that you can make your gateway properly interoperate with it.