Microsoft Exchange Server uses clients and servers to accomplish tasks across the network. Exchanging e-mail is similar to using the postal service to send a letter. For example, when a client application sends a message, the server acts as a central post office and routes the message to its destination. Users access messages in their mailbox by using their client e-mail application. When sending mail, the sender only needs to know the address of the recipient, not the details of how the message reaches its destination.
The main components of Microsoft Exchange Server work together in a similar way. When you use Microsoft Exchange Server to send a message, the message is first delivered to a central postoffice called the information store. The information store then determines where the message should be delivered by searching in the directory, which is similar to an address book. Finally, the mail carrier, or message transfer agent (MTA), delivers the message. Meanwhile, the system attendant, which is a background process, makes sure that the system runs smoothly and mail is routed correctly.
The following components provide essential services for Microsoft Exchange Server.
Directory Contains information about all objects in the system, such as servers, and recipients, such as users' mailboxes, public folders, and distribution lists. Recipients in the directory are also available in the Address Book so that users can look up addresses or information about other users quickly and easily.
Information store Contains the messages in users' mailboxes and public folders.
Internet Mail Service Routes messages between Microsoft Exchange Server and Simple Mail Transfer Protocol (SMTP)-based systems, including Internet mail servers and Post Office Protocol version 3 (POP3) and Internet Message Access Protocol, Version 4rev1 (IMAP4rev1) clients. For information about connecting to other systems, see Microsoft Exchange Server Concepts and Planning.
Message transfer agent (MTA) Routes messages to their destination.
System attendant A maintenance service that must be running for other services to run. It assists with tasks such as generating e-mail addresses and monitoring.