Overview of the Edge Transport Server Role

Applies to: Exchange Server 2010

In Microsoft Exchange Server 2010, the Edge Transport server role is deployed in your organization's perimeter network. Designed to minimize the attack surface, the Edge Transport server handles all Internet-facing mail flow, which provides SMTP relay and smart host services for the Exchange organization. Additional layers of message protection and security are provided by a series of agents that run on the Edge Transport server and act on messages as they're processed by the message transport components. These agents support the features that provide protection against viruses and spam and apply transport rules to control message flow.

The computer that has the Edge Transport server role installed doesn't have access to Active Directory. All configuration and recipient information is stored in Active Directory Lightweight Directory Services (AD LDS). To perform recipient lookup tasks, the Edge Transport server requires data that resides in Active Directory. This data is synchronized to the Edge Transport server using EdgeSync. EdgeSync is a collection of processes that are run on a computer that has the Hub Transport server role installed to establish one-way replication of recipient and configuration information from Active Directory to the AD LDS instance on an Edge Transport server. The Microsoft Exchange EdgeSync service copies only the information that's required for the Edge Transport server to perform anti-spam configuration tasks and the information about the connector configuration that's required to enable end-to-end mail flow. The Microsoft Exchange EdgeSync service performs scheduled updates so that the information in AD LDS remains current.

You can install more than one Edge Transport server in the perimeter network. Deploying more than one Edge Transport server provides redundancy and failover capabilities for your inbound message flow. You can load-balance SMTP traffic to your organization between Edge Transport servers by defining more than one mail exchange (MX) resource record with the same priority in the Domain Name System (DNS) database for your mail domain. You can achieve consistency in configuration between multiple Edge Transport servers by using cloned configuration scripts.

The message-processing scenarios that you can manage on the Edge Transport server role are described in the following sections.

Looking for management tasks related to managing transport servers? See Managing Transport Servers.

Internet Mail Flow

Servers that run the Edge Transport server role accept messages that come into the Exchange 2010 organization from the Internet. After the messages are processed by the Edge Transport server, they are routed to Hub Transport servers inside the organization.

All messages that are sent to the Internet from the organization are routed to Edge Transport servers after the messages are processed by the Hub Transport server. You can configure the Edge Transport server to use DNS to resolve MX resource records for external SMTP domains, or you can configure the Edge Transport server to forward messages to a smart host for DNS resolution.

For more information about mail flow, see Understanding Transport Pipeline.

Anti-Spam and Antivirus Protection

In Exchange 2010, the anti-spam and antivirus features provide services to block viruses and spam, or unsolicited commercial e-mail, at the network perimeter. Most viruses use spam-like tactics to gain access to your organization and to entice users to open an e-mail message. If you can filter out most of your spam, you're also more likely to capture viruses before they enter your organization.

Spammers use a variety of techniques to send spam into your organization. Servers that run the Edge Transport server role help prevent users in your organization from receiving spam by providing a collection of agents that work together to provide different layers of spam filtering and protection. Establishing tarpitting intervals on connectors makes e-mail harvesting attempts ineffective.

For more information about the anti-spam and antivirus features in Exchange 2010, see Understanding Anti-Spam and Antivirus Functionality.

Edge Transport Rules

Edge Transport rules are used to control the flow of messages that are sent to or received from the Internet. The Edge Transport rules help protect corporate network resources and data by applying an action to messages that meet specified conditions. These rules are configured for each server. Edge Transport rule conditions are based on data, such as specific words or text patterns in the message subject, body, header, or From address, the spam confidence level (SCL), or attachment type. Actions determine how the message is processed when a specified condition is true. Possible actions include quarantine of a message, dropping or rejecting a message, appending additional recipients, or logging an event. Optional exceptions exempt particular messages from having an action applied.

For more information about the Edge Transport rules, see Understanding Transport Rules.

Address Rewriting

You use address rewriting to present a consistent appearance to external recipients of messages from your Exchange 2010 organization. You configure the Address Rewriting agent on the Edge Transport server role to enable the modification of the SMTP addresses on inbound and outbound messages. Address rewriting is especially useful when a newly merged organization that has several domains wants to present a consistent appearance of e-mail addresses to external recipients.

For more information about address rewriting, see Understanding Address Rewriting.