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Transport Services

The high performance routing of email messages is one of the key features of Exchange Server. In the current version of Exchange, this routing is performed using the X.400 protocol. In Exchange 2000, SMTP has been implemented as the default transport protocol for routing all message traffic between servers, both within a site and between sites. The message routing algorithms have been significantly improved in Exchange 2000, which provides fault-tolerant delivery of messages. This feature increases throughput performance, especially for messaging traffic routed to the Internet.

Exchange 5.5 servers in a mixed environment will still use X.400 and RPC to communicate with the Exchange 2000 servers. Native Exchange 2000 no longer uses RPCs for communication; SMTP transport is now used instead. This change does mean that intraserver communication is no longer encrypted. Losing encryption at this higher layer is not so critical an issue because IPSEC is at a much better layer (lower) to provide secure communications. By encrypting the data stream at a lower layer, more of the upper layers can be secured.

The old X.400 Mail Transfer Agent (MTA) is not configured by default, but is still in the product for backward compatibility with Exchange 5.5, and for connectivity to other X.400 systems. Routing between bridgehead servers across routing groups can also be done via X.400 using the legacy MTA.

The SMTP service delivers to the New Technology File System (NTFS) queue. The queue can be found in the file system directory \exchsrvr\mailroot\queue. In the future, this may change to direct delivery into the store.

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