Understanding how Exchange routes Messages

Within the organization, Hub Transport servers use the information about sites stored in Active Directory to determine how to route messages, and they can also route messages across site links. The Hub Transport server does this by querying Active Directory about its site membership and the site membership of other servers, and then it uses the information it discovers to route messages appropriately. Because of this, when you are deploying an Exchange Server 2010 organization, no additional configuration is required to establish routing in the Active Directory forest.

For mail delivery within the organization, additional routing configuration is necessary only in these specific scenarios:

• If you deploy Exchange Server 2010 in an existing Exchange Server 2003 organization, you must configure a two-way routing group connector from the Exchange routing group to each Exchange Server 2003 routing group that communicates with Exchange Server 2010. You must also suppress link state updates for the same.

• If you deploy an Exchange Server 2010 organization with multiple forests, you must install Exchange Server 2010 in each forest and then connect the forests using appropriate cross-forest trusts. The trust allows users to see address and availability data across the forests.

• In an Exchange Server 2010 organization, if you want direct mail flow between Exchange servers in different forests, you must configure SMTP send connectors and SMTP receive connectors on the Hub Transport servers that should communicate directly with each other.

The organization’s Mail Transport servers handle mail delivery outside the organization and receipt of mail from outside servers. You can use two types of Mail Transport servers: Hub Transport servers and Edge Transport servers. You deploy Hub Transport servers within the organization. You can optionally deploy Edge Transport servers in the organization’s perimeter network for added security. Typically a perimeter network is a secure network set up outside the organization’s private network.

With Hub Transport servers, no other special configuration is needed for message routing to external destinations. You must configure only the standard mail setup, which includes identifying DNS servers to use for lookups. With Edge Transport servers, you can optimize mail routing and delivery by configuring one-way synchronization from the internal Hub Transport servers to the perimeter network’s Edge Transport servers. Beyond this, no other special configuration is required for mail routing and delivery.

Source of Information : Microsoft Press - Exchange Server 2010 Administrators Pocket Consultant