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Messages destined for an MS Mail postoffice available over an asynchronous or X.25 connection are retrieved by a connector MTA and delivered to the External or Multitasking MTA program that services the destination postoffice.
If the message is not retrieved by any instance of the connector MTA, it remains in the connector postoffice until it is retrieved by a LAN-connected instance of the MS Mail External or Multitasking MTA program or an MS Mail gateway installed on the connector postoffice. Otherwise, the message expires and returns to the sender.
The type of connection between indirect postoffices has no effect on message routing. However, if you want to set up a direct asynchronous or X.25 connection between the Microsoft Mail Connector and an MS Mail postoffice, you must set up an instance of the MS Mail External or Multitasking MTA program on the same LAN as the MS Mail postoffice. This program must be configured to connect over asynchronous or X.25 connections and typically requires a dedicated computer.
The following illustration shows how the External program is used when connecting a remote MS Mail postoffice to a Microsoft Exchange Server computer across an asynchronous connection:
The External or Multitasking MTA program provides the message transfer and modem management functions necessary to communicate over a remote connection. To create this type of connection, you must:
In many cases, you can set up this type of connection to integrate Microsoft Exchange Server with an existing MS Mail system without making significant changes to the configuration.