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Exchange Server 5.5 Core Components 

Added: 01/22/2002, Hits: 3,602, Rating: 0, Comments: 0, Votes: 0
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By Brian Talbert

Microsoft Exchange Server 5.5 consists of four "core" components. These are the System Attendant, the Directory Service, the Message Transfer Agent, and the Information Store. Each of these components are implementing in NT as a multi-threaded service.

The following discussion briefly describes the role of each and the relationship that each has with the others. More detailed configuration items are available in other articles.

System Attendant (SA)
The SA is primarly responsible for:
  • Creating Email Addresses for new Recipients.

  • Building Routing Tables.

  • Handles Message Tracking Functions.

  • Link Monitoring and Server Monitoring.

  • Reclaiming Lost Disk Space (from deleted directory objects).

The SA must be started before any of the other Exchange services will start. It is also good to note that there are issues with the SA service that cause a system to take an inordinately long period of time to shutdown. It is therefore best to stop the SA service prior to a shutdown.

Directory Service (DS)
The Directory Service provides all information pertaining to the various objects within exchange, such as mailboxes, folders, distribution lists, site containers, etc. It is similar in concept to a telephone directory that contains information about the various telephone subscribers, such as name, phone number, and address.

Each Exchange server maintains a complete copy of the directory for a particular site.. A process called directory replication is responsible for ensuring that each server within a site is updated properly. It is also possible to configure replication between sites.

Some directory information, such as user-related properties, are made available in the Global Address Book (GAL). The GAL is a subset of the directory and is much like your personal "little black book".

The actual DS database is kept in a file called DIR.EDB, which is stored, by default, in the EXCHSRVRDSADATA directory.

The DS is based upon the the CCITT x.500 standard for global directory services.

Information Store (IS)
The Information Store is responsible for the actual server-side storage of message data. It is also responsible for the delivery of LOCAL email... that is email destined for the SAME server on which the IS is running. The IS is comprised of two databases, the Private Store and the Publice Store. These two databases are maintained on the same server by default, though they can be seperated for performance benefits.
  • Private Store: Contains messages and data that are intended for a specific recipient such as an individual user or group of users. The messages within a users INBOX, for instance, would be in the Private Store. (Note: It is also possible for a user to specify that their mail be stored in a Personal Store, but this is not maintained directly by the IS and is NOT the default configuration.

  • Public Store: Contains messages and data that have been sent to a public folder. Public folders are like "shared" message centers that many users can access. Similar in concept to a "newsgroup" or "bulletin board system (BBS)".

The actual files comprising the IS are the PRIV.EDB and the PUB.EDB, found in the default directory of EXCHSRVRMDBDATA.

Message Transfer Agent (MTA)
In a nutshell, the MTA is responsible for the routing of messages. It routes messages within a site, and between sites. It may also translate and route messages to foreign (non-Exchange) systems. It is also responsible for the expansion of distribution lists.

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