Transport rules consist of a condition, an exception, and an action. Most transport rules have at least one condition and at least one action. You can also use exceptions to better target transport rules to specific messages. However, both conditions and exceptions are optional. Actions, on the other hand, are required. The following list describes conditions, exceptions, and actions:

• Conditions   Transport rule conditions are used to indicate which e-mail message attributes, headers, recipients, senders, or other parts of the message are used to identify the e-mail messages to which a transport rule action should be applied. All the conditions that you configure on a transport rule must be matched for the transport rule action to be applied. If you don't configure any conditions on a transport rule, the configured transport rule action is applied to all messages the transport rule encounters.
  For a list of conditions that you can use with transport rules, see Transport Rule Predicates.
  
• Exceptions   Transport rule exceptions resemble transport rule conditions. However, unlike transport rule conditions, exceptions identify the e-mail messages to which a transport rule action should not be applied. Transport rule exceptions override conditions and prevent a transport rule action from being applied to an e-mail message, even if the message matches all configured transport rule conditions. Only one transport rule exception has to be matched to override any transport rule conditions that have been matched.
  For a list of exceptions that you can use with transport rules, see Transport Rule Predicates.
  
• Actions   Actions are applied to e-mail messages that match all the conditions and none of the exceptions that are present on transport rules. Each action affects e-mail messages in a specific way, from redirecting the e-mail message to another address to dropping the message.
  For a list of actions that you can use with transport rules, see Transport Rule Actions.
  

For more information about conditions, exceptions, and actions, see Understanding How Transport Rules Are Applied in an Exchange 2007 Organization.

As I mentioned earlier, transport rules that run on Hub Transport servers are designed to help you manage compliance-related and policy-related issues. The conditions and exceptions that are available on Hub Transport servers query the Active Directory directory service, thus enabling you to reference distribution groups and other recipient objects and message classifications for ease of administration. For example, you can use distribution groups together with transport rules to easily customize a transport rule to address a business need such as controlling which groups can communicate with one another by e-mail.

Because Exchange 2007 stores the configuration of transport rules that reside on Hub Transport servers in Active Directory, all the Hub Transport servers in your organization have access to the same transport rule configuration. This means that you only have to configure a transport rule on one Hub Transport server. The transport rule configuration is replicated through Active Directory to all other Hub Transport servers in your organization automatically. This ensures that all Hub Transport servers in your organization are using the same transport rule configuration.

For more information, see the following topics:

• Transport rules on Hub Transport servers   See the "Transport Rules Agent" section in Overview of Transport Rules.
  
• Transport rule replication   See the "Transport Rule Replication" section in Understanding How Transport Rules Are Applied in an Exchange 2007 Organization.
  

Transport rules that run on Edge Transport servers are designed to help you manage the number of unwanted messages that enter your organization. Therefore, the set of conditions, exceptions, and actions on an Edge Transport server differs from the set that is available on Hub Transport servers. If your internal network is compromised, the Edge Transport rule agent can also apply the same or different rules to outgoing messages. Transport rules that run on Edge Transport servers are especially helpful during a new virus outbreak when antivirus definition files have not yet been updated to detect the new virus. If infected messages have known patterns that can be detected, you can configure transport rules on Edge Transport servers to block the messages from entering or leaving your organization.

Edge Transport servers each contain their own settings and do not replicate that configuration to other Edge Transport servers or back to Hub Transport servers in the Exchange 2007 organization. Also, while some configuration is replicated by using the Microsoft Exchange EdgeSync service from Hub Transport servers to Edge Transport servers, the transport rule configuration is not included. Therefore, if you have multiple Edge Transport servers and you want the same transport rules on each server, you must configure the transport rules on each Edge Transport server.

For more information about transport rules on Edge Transport servers, see the "Edge Rules Agent" section of Overview of Transport Rules.

In the Exchange Management Console, you can create and modify transport rules by using the Transport Rule wizard that functions much like Rules and Alerts in Microsoft Outlook. You can continue through the wizard pages and on each page, select conditions, actions, and then exceptions to build your transport rule. The following figure shows a rule constructed by using the Transport Rule wizard on a Hub Transport server:

For more information about how to configure a transport rule, see Managing the Transport Rules Agent.

The Exchange Management Shell is a new administrative interface available in Exchange 2007. The Exchange Management Shell lets you administer any Exchange 2007 feature. This includes some that can't be administered by using the Exchange Management Console.

For more information about the Exchange Management Shell, see Using the Exchange Management Shell.

In the Exchange Management Shell, you can create and modify transport rules by using several commands that, when they are run, create or modify a transport rule. Each command builds on the previous command to construct the conditions, exceptions, and actions that make up a transport rule. The following figure shows the transport rule that was constructed by using the Transport Rule wizard on a Hub Transport server in the earlier figure, but in this figure, the rule is created by using the Exchange Management Shell on a Hub Transport server.

For more information about how to configure a transport rule, see Managing the Transport Rules Agent.

Because Edge Transport servers do not replicate settings between one another, it can be time-consuming to manually duplicate transport rule configurations on each Edge Transport server. However, you can use the Export-TransportRuleCollection and Import-TransportRuleCollection cmdlets to more easily duplicate transport rule configurations on multiple Edge Transport servers.

When you run the Export-TransportRuleCollection cmdlet on an Edge Transport server, the transport rule configuration for that server is saved to an XML file. You can then use the Import-TransportRuleCollection cmdlet to copy and import this XML file to other Edge Transport servers. When you use the Import-TransportRuleCollection cmdlet to import the transport rule configuration stored in the XML file, any preexisting transport rules that were configured on that Edge Transport server are overwritten.

For more information, see Export-TransportRuleCollection and Import-TransportRuleCollection.

An ethical wall is a zone of non-communication between distinct departments of a business or organization to prevent conflicts of interest that might result in the inappropriate release of sensitive information.

You can use transport rules to create an ethical wall between recipients and senders in your organization. When an ethical wall transport rule is created and senders try to send messages to recipients on the other side of the ethical wall, the message is rejected and a non-delivery report (NDR) is returned to the sender. For more information about ethical walls, see the following topics:

• Understanding Ethical Walls
  
• How to Configure an Ethical Wall
  

New viruses threaten organizations everyday. Antivirus vendors and administrators must react to these virus threats as soon as possible to minimize the damage caused by viruses.

An administrator can use transport rules that run on Edge Transport servers to detect a message that has characteristics that the administrator has specified to determine whether the message is infected by a virus. When you create transport rules to look for specific characteristics, you can provide additional protection to your organization while you wait for antivirus vendors to provide a solution.

For more information about how to use transport rules to help manage antivirus threats, see Configuring Edge Transport Rules to Manage Viruses.

Disclaimers are blocks of text that can be prepended or appended by transport rules to messages that pass through Hub Transport servers. Disclaimers typically contain handling instructions or information that an organization wants applied to any message that enters or leaves the organization or is sent to, from, or between recipients and senders.

Because you use transport rules to apply disclaimers, you can use all the conditions and exceptions available on Hub Transport servers to control which messages disclaimers are applied to.

For more information about how to use transport rules to add disclaimers to messages, see How to Configure a Disclaimer.