Information Store

The information store maintains and provides access to the message database. The information store is visible to users as Inboxes and folders in the Microsoft Outlook client. It can store all types of information, including word processing documents, spreadsheets, and messages.

The information store maintains information in two databases ¾ the private information store (which contains user mailboxes) and the public information store (which contains public folders). It uses single-instance storage of messages, which means that a message sent to many recipients is stored only once on the server. This conserves disk space.

A server can have both a private information store and a public information store, or it can be dedicated to providing only one of these services. Dedicating a server to one of these functions can significantly improve performance for users. To make a server a dedicated mailbox server, delete the public information store; to make it a dedicated public folder server, delete the private information store.

When the information store receives a request to access a message, it performs the following tasks:

• Determines whether the message is already in memory (the buffer).
• Searches the message database for the message if the message is not already in memory.
• Returns the requested message or a "not found" message to the requesting client.

When the information store receives a message that a user on the local server wants to send, it performs the following tasks:

• Resolves individual addresses.
• Logs the message in the information store transaction log.
• Queries the MTA and directory to expand distribution lists if a message is addressed to users on the same server.
• Writes the message to the user's Inbox and notifies the client application.
• Applies rules the recipient has set when the message is delivered to the user's Inbox.
• Forwards the message to the MTA for routing, if the recipient is on another server.

Users, administrators, and applications all have access to the information store.

Users Users have access to information store objects (such as messages) and to private and public folders.

Administrators Administrators have access to the information store through the Administrator program, and they have permissions to perform the following tasks:

• Create or delete mailboxes.
• Modify the attribute values of information store objects.
• Create and modify permissions on public and private folders.

Applications Other applications running on Windows NT Server have access to and are accessible by the information store. The information store must have access to the directory or MTA to complete the following tasks:

• Requesting address information from the directory to resolve addresses or expand distribution lists
• Retrieving messages requested by users
• Forwarding messages it receives for other Microsoft Exchange Server computers to the MTA for routing
• Forwarding messages for foreign gateways through the appropriate connector for delivery

The information store's memory cache increases performance by maintaining the most recently requested messages in memory rather than reading them from the hard disk for every request. This buffer allows quick access to a message that has been read or modified recently in subsequent requests.

When a message is created, modified, or deleted, the information store records the transaction in a log file. The log is written sequentially to increase performance. If the server fails before changes are written to the database, the information store uses this log to restore those changes.