Understanding Edge Transport Servers in Exchange 2003 Hybrid Deployments

Applies to: Exchange Server 2010 SP3, Exchange Server 2010 SP2

Edge Transport servers in Exchange 2010 are deployed in your organization’s on-premises perimeter network. They’re non-domain-joined computers that handle Internet-facing mail flow and act as an SMTP relay and smart host for Exchange servers in your internal network. In hybrid deployments, you have the option of deploying Edge Transport servers running Service Pack 3 (SP3) for Exchange 2010 if you don’t want to expose internal hybrid Hub Transport servers directly to the Internet.

Learn more at: Overview of the Edge Transport Server Role

Adding an Edge Transport Server to a Hybrid Deployment

Deploying an Edge Transport server in your on-premises organization when you configure a hybrid deployment is an optional step. During the initial run of the Manage Hybrid Configuration wizard, the wizard requires that you select one or more Hub Transport servers. However, after the initial run of the wizard, you can add an Edge Transport server to your organization, configure it, run the Manage Hybrid Configuration wizard again, and then manually update the on-premises Send connectors and Edge Transport Receive connector to add it to the hybrid deployment.

When you add an Edge Transport server to your hybrid deployment, it communicates with Microsoft Exchange Online Protection (EOP) on behalf of the internal hybrid Hub Transport servers. The Edge Transport server acts as a relay between the on-premises hybrid Hub Transport server and EOP. All connection security previously handled by the hybrid Hub Transport server is handled by the Edge Transport server. Recipient lookup, compliance policies, and other message inspection, continue to be done on the hybrid Hub Transport servers.

If you add an Edge Transport server to your hybrid deployment, you don’t need to route mail sent between on-premises users and Internet recipients through it. Only messages sent between the on-premises and Exchange Online organizations will be routed through the Edge Transport server.

Mail Flow without an Edge Transport Server

The following process and diagram describe the path messages take between an on-premises organization and Exchange Online when there is no Edge Transport server deployed:

1. Messages from the on-premises organization to recipients in the Exchange Online organization are sent from the Exchange 2003 server to a hybrid Hub Transport server.

2. The Hub Transport server sends the message directly to the Exchange Online EOP company.

3. EOP delivers the message to the Exchange Online organization.

4. Messages sent from the Exchange Online organization to recipients in the on-premises organization follow the reverse route.

Mail flow in a hybrid deployment without an Edge Transport server deployed

Mail Flow with an Edge Transport Server

The following diagram shows the path messages take between an on-premises organization and Exchange Online when there is an Edge Transport server deployed. Messages from the on-premises organization to recipients in the Exchange Online organization are sent from the Exchange 2003 server:

1. Messages from the on-premises organization to recipients in the Exchange Online organization are sent from the Exchange 2003 server to a hybrid Hub Transport server.

2. The Hub Transport server sends the message to an Edge Transport server.

3. The Edge Transport server sends the message to the Exchange Online EOP company.

4. EOP delivers the message to the Exchange Online organization.

5. Messages sent from the Exchange Online organization to recipients in the on-premises organization follow the reverse route.

Mail flow in a hybrid deployment with an Edge Transport server deployed

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