Platform SDK: Exchange Server

Gateways and Backboning

All Microsoft Exchange Server gateways should support backboning. A gateway must transfer both message content and addressing information in the appropriate format for the receiving system.

Transferring Message Content

Some foreign systems do not support the special properties that Microsoft Exchange Server allows, such as Microsoft Schedule+ menu formats and rich text in messages. A gateway must be able to distinguish between three types of recipients and handle message content accordingly. A message recipient can be on:

A foreign system that does not support special properties. For example, the message may be addressed to an Internet user.
Another Microsoft Exchange Server site that is connected by a foreign system as a backbone.
A foreign system that uses a MAPI client and therefore supports special properties.

For destination systems that support special properties, the gateway must encapsulate the message content so that it can pass through the foreign system backbone and then be re-created with all its properties at the destination system.

Transferring Addressing Information

Addressing formats must be translated between different systems. When a message is sent from a Microsoft Exchange Server system, the addresses of both the sender and the recipient are in Microsoft Exchange Server native format, which is called EX and is the X.500 distinguished name (DN). The gateway must translate both these addresses to the format of the backboning system.

When the message is transferred from the foreign system backbone to the Microsoft Exchange Server recipient, the gateway that makes that transfer must translate the recipient’s address back to the original Microsoft Exchange Server format. To convert the sender’s address back to the original format, the gateway must open the original message that is attached to the message transfer envelope (MTE). The gateway must also be able to handle address translation for CC and BCC recipients. See Addressing for details about address translation.