When Exchange can??™t connect to the next
hop in a routing path, it tries to reroute the
message over an alternative path.
When a message is being sent to multiple recipients,
Exchange delays message splitting until a
fork in the routing path is reached. This behavior
is known as delayed fan-out.
When a message is being sent to multiple
recipients, message splitting occurs
immediately after recipient resolution.
Each Hub Transport server queries Active
Directory separately to retrieve the routing
configuration used to calculate a routing table
and to receive configuration updates.
Exchange uses a link state table to store a
routing table and advertises configuration
changes by using link state updates. The
routing group master retrieves updates
from Active Directory and coordinates the
propagation of link state changes that are
learned by servers in its routing group.
Basics of Exchange Server 2007 Routing
One of the most important changes in Exchange Server 2007 is the way basic mail routing is handled.
Unlike in previous versions of Exchange, all mail now must flow through a Hub Transport server role.
For example, in Exchange 2003, two users mailing each other on the same mailbox servers would never
route through a bridgehead. This is an important change because now Exchange can guarantee that
every message can have transport rules applied.
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