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Deployment Options for Edge Transport Servers

 

Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007

Topic Last Modified: 2007-09-24

This topic describes the options for deploying a Microsoft Exchange Server 2007 Edge Transport server role in your existing Exchange Server topology. In addition, the topic explains what to consider when you configure a server that is running Microsoft Internet Security and Acceleration (ISA) Server 2006 as a firewall between your Edge Transport server and Hub Transport server.

Designed to minimize the attack surface, the Edge Transport server handles all Internet-facing mail flow, which provides Simple Mail Transfer Protocol (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 are 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 following deployments are supported:

  • Deploy an Exchange 2007 Edge Transport server into an existing Exchange Server 2003 environment. For more information, see How to Deploy an Edge Transport Server in an Existing Exchange Server 2003 Organization.

  • Recommended topology: Deploy an Exchange 2007 Edge Transport server in an Exchange 2007 organization in a perimeter network, which is also known as the boundary network or screened subnet, as part of a workgroup or domain. For more information, see How to Perform a Custom Installation Using Exchange Server 2007 Setup.

  • Deploy an Exchange 2007 Edge Transport server as a member of the Exchange 2007 organization that has the Active Directory directory service.

  • Deploy more than one Exchange 2007 Edge Transport server in an Exchange 2007 organization in the perimeter network of a domain or workgroup.

The recommended option is to deploy the Edge Transport server role outside the Exchange organization in an organization's perimeter network. The Edge Transport server can be deployed as a stand-alone server or as a member of a perimeter Active Directory domain.

For more information about how to deploy an Edge Transport server in an Exchange 2007 organization in a perimeter network, see the following topics:

The following table lists the advantages of the different types of Edge Transport server deployment.

 

Edge Transport server deployment Advantage

As part of a domain

Less secure, easy to manage

As a stand-alone server

More secure, more difficult to manage

As part of a workgroup

More secure, more difficult to manage

As a special perimeter forest

More secure and easy to manage but requires more hardware support (recommended for large enterprises)

noteNote:
You don't have to deploy the Edge Transport server role to deploy Exchange 2007. You can have a single computer that is running the core server roles, such as the Mailbox, Client Access, and Hub Transport server roles, accepting Internet e-mail for your domain and running anti-spam and antivirus programs on that computer.

When you install an Edge Transport server, you enable anti-spam functionality on that server. When you add an Edge Transport server to your Exchange 2007 perimeter network, you must subscribe the Edge Transport server to an Active Directory site by using the Edge Subscription process if either of the following conditions is true:

  • You plan to use the anti-spam features, recipient lookup, or safelist aggregation,

  • You plan to deploy Domain Security with a partner organization.

When you deploy more than one Edge Transport server in an Exchange 2007 organization in the perimeter network of a domain or workgroup, you can load-balance SMTP traffic among all Edge Transport servers by defining more than one MX resource record with the same priority in the Domain Name System (DNS) database for your mail domain. Deploying more than one Edge Transport server also provides fault tolerance.

The following table compares features that are available for the different deployment options for Edge Transport servers in an Exchange 2007 organization.

Deployment options for Edge Transport servers

  Edge Transport server is not deployed Edge Transport server is deployed in an Active Directory forest that services the Exchange organization Recommended: Edge Transport server role is deployed in the perimeter workgroup or perimeter domain Comments or description

Minimum number of servers

1

2

2

The Edge Transport server role cannot be installed on the same computer as the other server roles. In the single-server scenario, anti-spam agents are manually deployed on the Hub Transport server role. The Edge Transport server role is not installed.

Network isolation

No

No

Yes

Spam and malware are rejected before they enter the network only if the Edge Transport server role is deployed at the perimeter network.

Anti-spam agents installed by default

No

Yes

Yes

If the Edge Transport server role is not deployed, an administrator can enable anti-spam agents on the Hub Transport server role by running an Exchange Management Shell command. For more information, see How to Enable Anti-Spam Functionality on a Hub Transport Server.

Anti-spam user interface

Anti-spam user interface is not visible by default. It is enabled after anti-spam agents are deployed manually.

Visible by default

Visible by default

The Exchange Management Console provides a user interface for configuring the following:

  • Anti-spam functionality

  • Receive connectors

  • Send connectors

  • Transport rules

Internet e-mail processing

Internet e-mail processing is enabled only after you set the Internet usage type on the Receive connector, and create a new Send connector with the Internet usage type.

Yes

Yes

For more information, see How to Configure Connectors for Internet Mail Flow.

Connection Filtering

Yes

Yes

Yes

Connection filtering provides IP Block lists and IP Allow lists to protect against spam. For more information, see Connection Filtering.

Sender Filtering

Yes

Yes

Yes

Sender reputation is dynamically analyzed and updated over time. For more information, see Sender Filtering.

Recipient Filtering

Yes

Yes

Yes

Recipients are validated by using the global address list (GAL). For more information, see Recipient Filtering.

Microsoft Exchange EdgeSync service

Not applicable

Yes

Yes

Microsoft Office Outlook Safe Senders lists and the GAL are pushed in encrypted format to the network perimeter.

Sender ID

Yes

Yes

Yes

Sender ID is checked when e-mail is received and included in spam rating. For more information, see Sender ID.

Content Filtering (Intelligent Mail Filtering)

Yes

Yes

Yes

Regular Microsoft SmartScreen updates help counter spam and phishing threats. For more information, see How to Configure Anti-Spam Automatic Updates.

Spam confidence level

Yes

Yes

Yes

A spam confidence level (SCL) rating is assigned to a message, based on several factors. For more information, see Adjusting the Spam Confidence Level Threshold.

Anti-spam stamp

Yes

Yes

Yes

Messages are stamped with details of spam assessment. For more information, see Anti-Spam Stamps.

Back pressure and tarpitting

Yes

Yes

Yes

Back pressure and tarpitting protect against denial of service and directory harvest attacks. For more information, see the Understanding Back Pressure and the "Tarpitting Functionality" section of Recipient Filtering.

Two-tiered spam quarantine

Yes

Yes

Yes

An administrator can access the spam quarantine folder and release a message to its recipient. For more information, see Spam Quarantine.

Attachment Filtering

No

Yes

Yes

Attachments are removed based on size, content, or file type. For more information, see Attachment Filtering.

Forefront Security for Exchange Server

Yes

Yes

Yes

For more information, see Protecting Your Microsoft Exchange Organization with Microsoft Forefront Security for Exchange Server.

Depending on the network adapter (also known as NIC) configuration or firewall configuration in your perimeter network topology, you can deploy an Edge Transport server as a multi-homed bastion host configuration or as a single-homed, or screened subnet, configuration as shown in the following figure.

Network configurations for multi-homed and a single-homed Edge Transport servers

Multihomed, Singlehomed Edge Configuration

In a multi-homed configuration, a host is connected to two or more networks or has two or more network addresses. In a single-homed configuration, there is a single firewall with three network adapters or NICs. This is generally known as a triple-homed firewall.

In both the multi-homed configuration and the single-homed configuration, you can have one or more IP addresses to configure Send connectors and Receive connectors accordingly on your Edge Transport servers and Hub Transport servers. For more information about how to configure connectors, see Managing Connectors.

You can configure an Edge Transport server or Hub Transport server together with Microsoft Internet Security and Acceleration (ISA) Server 2006 to protect your corporate network and applications. For more information about how to configure an ISA Server 2006 firewall between your Hub Transport servers and Edge Transport servers, see Using ISA Server 2006 with Exchange 2007.

When you configure ISA Server 2006 in your Exchange organization with Edge Transport servers and Hub Transport servers, if you want to allow SMTP or SMTPS (secure SMTP) traffic to flow between Edge Transport servers and Hub Transport servers, follow these guidelines:

  • If SMTP traffic from the Edge Transport server to the Hub Transport server is being filtered through the server that is running ISA Server 2006, disable the SMTP filter on that server.

  • If SMTPS traffic from the Edge Transport server to the Hub Transport server is being filtered through the server that is running ISA Server 2006, disable the SMTP filter for this option on that server too.

Or, if you don't want to disable SMTP or SMTPS filtering on the server that is running ISA Server 2006, you can add SMTP verb commands, such as X-ANONYMOUSTLS and X-EXPS, which are unique to Exchange 2007, to the SMTP filter add-in on ISA Server 2006.

For more information about how to disable SMTP or SMTPS filtering on ISA Server 2006 or how to add SMTP verb commands to ISA Server 2006, see Messages Queue on an Edge Transport Server with 500 5.1.1 Unrecognized Command Error.

 
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