About Rules

Microsoft Exchange Server uses rules to automatically execute predefined actions on selected objects. You can also develop applications that use rules to carry out predefined or custom actions. For example:

• Rules can be triggered when mail arrives at a user's mailbox or items are sent or posted to a public folder. These rules can set up or control an often-used combination of condition and action.
• Rules can perform a part of an application's activity, such as setting up folder structures.

For more information on developing applications that use rules, see Working with Rules.

A rule can be set up to run on either Microsoft Exchange Server or on the Microsoft Exchange Client. All rules on the client are known as deferred action rules. Rules on the server are of the following two types:

• Rules on Public folders A predefined, limited set of rules.
• Rules on Mailboxes The predefined rules, as well as custom actions that are invoked by mailbox rules. Custom actions take place on the Microsoft Exchange Client through the deferred action mechanism.

The mechanism for rules includes the following:

• Server rules engine Part of the information store process that monitors messages that are sent to other users or posted to public folders.
• Client interface The interface used for setting rules and for carrying out deferred actions.
• IExchangeModifyTable interface An interface similar to an IMAPITable interface that is capable of handling the condition and action structures of rules.
• IExchangeRuleAction interface An interface used to retrieve actions from deferred action messages.
• IExchangeRuleExt interface and IExchangeRuleExtCallback interface Interfaces that provide users with custom deferred actions that can be selected from the Microsoft Exchange Client interface.