Exchange Terminology


Topic Last Modified: 2006-09-14

advanced queuing engine

A core component of the SMTP transport subsystem in Microsoft® Exchange Server 2003. It passes the messages from message queue to message queue, invoking event sinks, such as categorizer and routing engine, as needed to transfer the messages to their destinations.

body part

Defines the content type of an X.400 message. A single message can include multiple body parts for the actual message and message attachments. Body parts are identified by an object identifier.

bridgehead server

A computer that connects servers using a connector so that information can be passed from one server to another. In Exchange 2003 and Exchange 2000 Server, a bridgehead server is a connection point from a routing group to another routing group, remote system, or other external system.


An internal component of the SMTP transport subsystem in Exchange 2003 that processes all messages that pass through the server. The categorizer resolves sender and recipient information against Active Directory, expands distribution lists, checks restrictions, applies per-sender and per-recipient limits, and bifurcates messages if multiple copies must be created (for example, if recipients require different message formats).


A calculated value that is used to test data for the presence of errors that can occur when data is transmitted or when it is written to disk. The checksum is calculated for a given chunk of data by sequentially combining all of the bytes of data with a series of arithmetic or logical operations. After the data is transmitted or stored, a new checksum is calculated in the same way using the (possibly faulty) transmitted or stored data. If the two checksums do not match, an error has occurred, and the data should be transmitted or stored again. Checksums cannot detect all errors, and they cannot be used to correct erroneous data.


A component that enables information to flow between two systems. For example, connectors support message transfer, directory synchronization, and calendar querying between Exchange and other messaging systems. When two systems are in place, the basic user experience is maintained on both messaging systems. The exchange of mail and other information between Exchange and other messaging systems is transparent to the user, even if the two systems function differently.

Exchange store driver

A component in Exchange 2003 that enables the SMTP service to communicate with the Microsoft Exchange Information Store service.

foreign domain

A directory object that defines a messaging environment that is external to the local messaging system and uses different message formats and communication protocols. Foreign domains are used for addressing and routing purposes. The external messaging system is usually connected to the local messaging system using a gateway connector.

foreign messaging system

A messaging system that uses different message formats and communication protocols than the local messaging system. For example, Novell GroupWise is a foreign messaging system for Exchange 2003.

hub and spoke topology

A topology in which a central node performs all routing for the other nodes in the environment. The central routing node is the hub, and the connections to all other nodes are the spokes.


A physical structure that builds the foundation of a network. For example, the physical structure of a computer network consists of cables, hubs, switches, routers, servers, and other resources that form the communication infrastructure of a company.

Internet Security and Acceleration (ISA) Server

A software application from Microsoft Corporation to increase the security and performance of Internet access for businesses. ISA Server provides an enterprise firewall and high-performance Web cache server to securely manage the flow of information from the Internet through the enterprise's internal network.

local delivery queue

A repository for messages that are awaiting local delivery to mailboxes in a mailbox store on the Exchange server through the Exchange store driver.

mail exchanger (MX) record

A database entry in a Domain Name System (DNS) zone that points to an SMTP host that is responsible for message transfer to an Internet domain.

post-categorization queue

A special message queue in the advanced queuing engine of the SMTP transport subsystem of Exchange 2003 for messages after they have been categorized. Messages in this queue might be delivered locally or passed to the routing engine to determine the next hop on the transfer path.

pre-categorization queue

A throttling queue in the advanced queuing engine for messages that are waiting for categorization by the categorizer.

pre-submission queue

A special message queue in the advanced queuing engine of the SMTP transport subsystem of Exchange 2003 that represents the entry point for all messages into the advanced queuing engine. Messages in this queue have not been processed yet.

queue manager

A component of the SMTP transport subsystem in Exchange 2003 that maintains the link queues in the transport subsystem.

routing engine

A component of the SMTP transport subsystem in Exchange 2003 that determines the next hop for messages on the transfer path to remote destinations.

smart host

An SMTP host that forwards e-mail messages on behalf of other SMTP hosts and Internet clients to the next hop on the way to their destinations. Internet service providers (ISPs) often provide their customers with a central smart host that handles message transfer across the Internet. If a smart host is designated, the Exchange server needs only to transmit messages to the smart host, and does not require a direct connection to the mail exchanger (MX) host of the destination domain. A smart host is also called a relay host, and a smart host that accepts messages from any source on the Internet and relays them to other destinations on the Internet is called an open relay. Open relays are often sources of unsolicited commercial e-mail (spam).

SMTP protocol engine

A component of the SMTP transport subsystem in Exchange 2003 that communicates through SMTP with remote hosts and Internet clients.


The physical arrangement or layout of a network infrastructure. The topology of a network can consist of local area network (LAN) connections, metropolitan area network (MAN) connections and wide area network (WAN) connections and the devices that connect these networks.

For additional definitions of Exchange 2003 terminology, see the Exchange Server 2003 Glossary.