The functionality you need to design for your specific gateway is determined by the characteristics of the mail systems it connects. The tasks performed by a typical gateway include the following:
Message transfer Delivery of messages to foreign message systems.
Address mapping Translating between Microsoft Exchange Server addresses and the address format of foreign message systems.
Message content translation Converting between the data formats used by Microsoft Exchange Server and foreign message systems. For example, performing RTF to plain text conversion.
Backboning Transparently connecting two Microsoft Exchange Servers by means of an intermediate foreign message system.
Performance monitoring Monitoring the performace of a gateway, both for self-tuning and for use by an administrator.
Event logging Recording events such as deliveries and error conditions to a log file.
Error handling Recovering gracefully from error conditions.
Message tracking Being able to generate appropriate delivery and non-delivery reports.
Configuration management Providing the administrator with a way to configure the gateway.
Directory synchronization Keeping the directories of two Microsoft Exchange Servers that are connected by the gateway synchronized with each other.
These tasks are described in the following sections.