The Edge Transport server role accepts mail coming into the Exchange 2007 organization from the Internet and routes all outbound messages to the Internet. The Edge Transport server role acts as a smart host and SMTP relay for the Exchange organization. You configure Send connectors and Receive connectors on the Edge Transport server to control message processing.

Most viruses use spam-like tactics to gain access to your organization and to entice users to open a piece of mail. If you can filter out most of your spam, or unsolicited commercial e-mail, you are more likely to capture viruses before they enter into your organization. Spammers use a variety of techniques to send spam into your organization. The Exchange 2007 Edge Transport server role helps 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:

• Attachment Filter agent   This agent filters messages based on attachment file name, file name extension, or file MIME content type. You can configure this agent to block a message and its attachment, to strip the attachment and allow the message to pass through, or silently delete the message and its attachment.
  
  
• Connection Filter agent   This agent filters messages based on the IP address of the remote server from which a message is sent. A variety of IP Block lists and IP Allow lists and optional services are used to determine what action, if any, to take on a particular message based on its source IP address.
  
  
• Content Filter agent   This agent uses Microsoft SmartScreen technology to assess the contents of a message. The Exchange Intelligent Message Filter is based on patented machine learning technology from Microsoft Research. The Intelligent Message Filter learns distinguishing characteristics of legitimate e-mail and of spam. Based on these characteristics, the Intelligent Message Filter helps determine whether an incoming message is spam or legitimate e-mail.
  
  
• Recipient Filter agent   This agent compares the recipients that are identified in the RCPT TO: SMTP header to known recipients identified in an IP Block list and to the local recipient directory which stores valid recipients that exist inside the organization to determine what action, if any, to take on a particular message.
  
  
• Sender Filter agent   This agent compares the sender identified in the MAIL FROM: SMTP header to known senders identified in an IP Block list to determine what action, if any, to take on a particular message.
  
  
• Sender ID agent   This agent relies on the RECEIVED: SMTP header and a query to the sending system's DNS service to determine what action, if any, to take on a particular message.
  
  

Many organizations have legal, regulatory, or internal requirements to filter, process, and store e-mail that is between users in the organization. Additionally, many organizations have additional requirements for how to handle mail sent to or from the Internet. A collection of messaging policy and compliance agents in Exchange 2007 helps organizations more easily comply with these legal, regulatory, and internal requirements by providing ways to configure rules and settings that help you meet these requirements. The following messaging policy and compliance agents are available on the Edge Transport server role:

• Address Rewrite agent   This agent enables the modification of the SMTP address for any sender or recipient of messages sent or received by your organization. Address rewriting can be useful in scenarios where an organization wants to hide internal domains, to enable multiple organizations appear as a single organization, or to integrate services that are provided to an organization by a third-party.
  
  
• Edge Rules agent   You configure the Edge Rules agent on the Edge Transport server role to create rules that 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, see the following topics:

• Transport Architecture
  
  
• Planning for Edge Transport Servers