Configuring the Hub
Transport Role
Exchange Server 2000/2003 used the concept of bridgehead servers and connectors. A bridgehead
server referred to an Exchange server that served as a connection point for delivering email from
one routing group to another and to remote or external email systems. Bridgehead servers used
connectors to make information flow between routing groups and remote or external systems
possible. Several types of connectors were available: SMTP, Routing Group, and X.400.
Exchange Server 2007 introduces the concept of the Hub Transport role. Computers running Exchange
Server 2007 with the Hub Transport role are called Hub Transport servers and are identical to
bridgehead servers in Exchange 2000/2003; however, they differ greatly in core transport
functionality. The Hub Transport server role is installed in any Active Directory site that contains the
Mailbox server role and is responsible for mail delivery within the Active Directory site. It can be
installed on separate hardware as the only server role or on the same server hardware in conjunction
with other non - clustered Exchange Server 2007 roles. The Hub Transport server receives messages
from and sends messages to servers running the Mailbox server role. Every message sent and received
by an Exchange mailbox must pass through the Hub Transport server, hence transport rules and
journal policies are not skipped for any message. In a multi - site organization, messages destined for a
user in a different site are transferred to a Hub Transport server in that site for delivery. Messages
destined for the Internet or other messaging systems are sent to the Edge Transport server for delivery.
We discuss the Edge Transport role further in Chapter 9 . The Hub Transport server role uses Send
Connectors and Receive Connectors for email routing and delivery.
This chapter covers:
Understanding the core transport architecture implemented by the Hub Transport and
Edge Transport servers.
Using and configuring the Hub Transport server
Configuring various types of connectors in Exchange Server 2007
Using email address policies and accepted domains
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Part II: Working with Server Roles
The Transport Server Architecture
The core transport architecture was rewritten in Exchange Server 2007 and is very different from
previous versions of Exchange. Those familiar with Exchange Server 2000/2003 might quickly notice
that transport is no longer dependent on Internet Information Server (IIS). In fact, it is required that you
uninstall the SMTP and NNTP services prior to installing Exchange Server 2007 unlike Exchange Server
2000/2003, which required both services to be installed. Additionally, all core components required for
message categorization, routing, and delivery are included in Exchange Transport Service with no
components dependent on IIS. This section briefly reviews the core transport architecture from the
perspective of the Management Shell.
The following Hub Transport related cmdlets are discussed:
A number of components make up the core transport architecture implemented by both the Hub
Transport server and Edge Transport server roles. These components as well as other processes and
queues constitute the transport pipeline in Exchange Server 2007. Think of it as a series of processes that
make message delivery or relay possible. Every message sent or received must go through the transport
pipeline. The transport pipeline consists of the following:
SMTP Receive: This component accepts connections on port 25 inbound to the Hub Transport
or Edge Transport servers. This component is controlled by the SMTP Receive Connector, which
is similar to the SMTP virtual server in Exchange Server 2000/2003. It is at this stage of the
transport pipeline that anti - virus and anti - spam agents are implemented to filter incoming con-
nections, message content, determine the sender, and apply any compliance or transport rules
configured. Actual message hygiene or transport rules performed vary slightly depending on
which server role is installed, either the Hub Transport role or Edge Transport role. A series of
events are triggered as the message is received and agents are executed against the message.
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