Designing Message Transport During Coexistence with Exchange Server 2003

To support coexistence between different versions of Exchange server, all servers running Exchange Server 2010 are added automatically to a single routing group when you install Exchange Server 2010. The Exchange Server 2010 routing group includes all Exchange Server 2010 servers, regardless of the Active Directory site in which they reside.

Integrating Exchange Server 2010 into Exchange Server 2003 Routing Groups

Exchange Server 2003 does not support AD DS sites for message routing, but rather implements routing groups for Exchange-specific routing decisions. During the coexistence phase of your planned upgrade, the Exchange Server 2010 servers are presented to Exchange Server 2003 servers as members of a single routing group called Exchange Routing Group (DWBGZMFD01QNBJR). When planning your upgrade to Exchange Server 2010, it is important that you consider these routing topology differences.

When you install Exchange 2010 Hub Transport server for the first time, you must specify an Exchange 2003 bridgehead server to establish the first routing group connector. You should select a bridgehead server that is located either in a hub routing group or in a routing group that has many mailboxes. The routing group connector links the routing group where the Exchange Server 2003 server resides with the Exchange Server 2010 routing group. From the perspective of the Exchange Server 2003 servers, the Exchange Server 2010 routing group includes all Exchange Server 2010 servers regardless of the AD DS site in which they reside.

The Exchange Server 2010 Hub Transport server that you install and the Exchange Server 2003 bridgehead that you select are configured as the source and target servers on two reciprocal routing group connectors. This routing group connector creates a single connection point between Exchange Server 2003 and Exchange Server 2010.

Supporting Multiple Routing Groups

However, if your existing Exchange Server 2003 organization includes multiple routing groups, you may wish to create additional connection points between Exchange Server 2003 and Exchange Server 2010 to optimize mail flow. Bear in mind that if you create multiple paths between the Exchange Server 2010 routing group and your legacy Exchange Server organization, you must suppress minor link-state updates to ensure that message looping does not occur when Exchange Server 2003 recalculates a route; when link state updates are suppressed, Exchange Server 2003 servers queues messages at point of failure, instead of recalculating the route, in a similar way to Exchange Server 2010.

Upgrade External Connectivity

The Edge Transport server role is designed to provide improved antivirus and anti-spam protection for the Exchange server organization. It also applies policies to messages in transit between organizations. You can deploy the Edge Transport server as a smart host and SMTP-relay server for an existing Exchange Server 2003 organization. You can add an Edge Transport server to an existing Exchange organization without upgrading the internal Exchange servers or making any organizational changes. You do not need to perform any AD DS configuration changes in advance of deploying an Edge Transport server as it is deployed outside AD DS. If you are using the Exchange Intelligent Message Filter in Exchange Server 2003 to perform anti-spam tasks, you can use the Edge Transport server to provide an additional layer of anti-spam protection.

Because you cannot enable Edge Synchronization, you must configure message routing on the internal Exchange bridgehead servers and the Edge Transport server manually, rather than using the Edge Subscription to configure the settings based on the internal Active Directory configuration. You will need to:

  • Configure the Exchange 2003 bridgehead servers to use the Edge Transport server as a relay for outbound Internet messages. To do this, configure the appropriate SMTP connector to send messages to the Internet using the IP address of the Edge Transport server as a smart host.
  • For inbound Internet messages, ensure that your organization’s mail exchange (MX) resource records reference the IP addresses of the Edge Transport servers.
  • Configure SMTP connectors to enable message routing between the Edge Transport servers and the Exchange 2003 bridgehead servers, and between the Edge Transport servers and Internet SMTP servers. At a minimum, you must configure an SMTP send connector for sending e-mail and an SMTP receive connector receiving e-mail from the Exchange 2003 servers, and configure a send connector for sending e-mail to Internet recipients. By default, a receive connector is configured on the Edge Transport server that will accept messages from the Internet SMTP servers.
  • Configure the accepted domains. The accepted domain setting specifies the SMTP domains that the organization uses. You must configure these domains manually on the Edge Transport server if you do not have the option of configuring an edge subscription.
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