Datasheet

Active Directory for Exchange Server 2007 15
The global catalog partition received many new items of information as a result of the
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installation of Exchange Server 2007 in a forest. Exchange uses the global catalog to
generate address lists for usage by Exchange recipients, and Exchange Server also uses
it to locate a recipient to aid in the delivery of mail items to that recipient. Exchange
Server automatically generates the global address list (GAL) from all recipients listed in
the global catalog.
Message Flow
In previous versions of Exchange Server, a complex link-state routing algorithm was used to
route messages between geographically separated Exchange servers. Exchange used routing
groups that were connected with routing-group connectors to perform this routing. With the
elimination of routing groups and link-state routing in Exchange Server 2007, all Exchange
message routing is performed by Hub Transport servers using the Active Directory sites and
site links that service Active Directory itself. As such, message routing (both within the same
site and across site links) is significantly less complex in Exchange Server 2007.
We will cover Exchange Server 2007 routing in Chapter 3, “Configuring the
Mailbox and Hub Transport Roles.”
Within each Active Directory site that contains a Mailbox server (or Unified Messag-
ing server), you must have at least one Hub Transport server. The Hub Transport server
is responsible for routing all messages within a site and between connected sites. Even a
message that is sent from a recipient on Server A to another recipient on Server A must first
cross through a Hub Transport server for delivery—a big change in message routing from
Exchange Server 2003. When messages must be routed between sites, the Hub Transport
server in the originating site determines the best route available at that time to the destina-
tion server and routes the message accordingly.
Message routing between sites occurs as detailed here:
1. The sending user submits the message to their mailbox on the Mailbox server.
2. The Mailbox server notifies a Hub Transport server in its Active Directory site that it
has a message awaiting pickup.
3. A Hub Transport server in the same Active Directory site as the originating Mailbox
server picks up (retrieves) the message from the Mailbox server.
4. The Hub Transport server performs a query against Active Directory to determine
what Mailbox server the recipient of the message is on.
5. The Hub Transport server then computes the lowest-cost route to the site containing
the destination Mailbox server based on the site link costs configured on site links
between the sites.
6. The Hub Transport server in the originating Active Directory site then sends the mes-
sage along the lower-cost route it has computed.