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Exchange 2010 Transport Fundamentals

Aug. 17, 2009
Rich Luckett

Exchange 2010 builds upon the significant changes to the transport that were made in Exchange 2007. In this article, I'll review the transport pipeline and routing components and list some of the new architectural and administrative enhancements to the Exchange 2010 transport.

Before you explore the new transport features in Exchange 2010 you may want to review some transport basics. The basic fundamentals to the Exchange 2010 transport will better help you understand and appreciate the new enhancements. Two of the key fundamentals are the Transport Pipeline and Routing. The transport pipeline is a collection of Exchange 2010 server roles, connections, components, and queues that work together to route all messages to the categorizer on a Hub Transport server inside the organization. Message routing topologies in Exchange 2010 and routing decisions are based on the existing Active Directory directory service site topology.

The pipeline’s job is to see that every single email delivered in an Exchange organization is categorized. If categorization does not complete than a message cannot be routed properly. Both the Edge Transport and the Hub Transport roles perform categorization. However, categorization on the Edge Transport is limited, for the most part, to inbound messages from a receive connector. The Hub Transport is more active as it needs to potentially categorize messages from Receive Connectors, Pickup Directory, Replay Directory, Store Driver and various Transport Agents. The core components and processes to the transport pipeline are:

SMTP Receive - A series of events that work together in a specific order to validate the contents of a message before it is accepted into the organization. This includes anti-spam and antivirus optionally.

Submission - The process of putting messages into the Submission queue. This is accomplished with Receive Connectors, Pickup directory or Replay directory, Store Driver submission, or transport agent.

Categorizer - Process in which the message is put directly in the delivery queue. The process involves: Recipient resolution, Distribution Group expansion, message Bifurcation, Routing resolution and Content conversion.

SMTP Send (Send Connector) - All messages that are sent to a different Active Directory site, to a mailbox that resides on a different version of Exchange, or to a mailbox that resides in a different Active directory Forest must be routed through a send connector.

Message routing in Exchange 2010 can be complex and requires a lengthy discussion. I’m not going to try to cover all the aspect of routing in this blog. However there are some key components to Exchange 2010 routing that belong in a fundamentals discussion.

Active Directory Sites - Used as a routing boundary for Hub Transport Servers

AD IP Site Links - Define logical routing paths and least cost routes between hub transports in different AD Sites.

Send Connectors - Primary used to route to external SMTP address space.

Routing Groups - Used as a routing boundary for Exchange 2003.

Routing Group Connectors - Define logical routing paths between Exchange 2010 and Exchange 2003.

Microsoft Exchange Transport Service - The Simple Mail Transfer provider for Exchange 2010 for inbound and outbound mail

Microsoft Exchange Active Directory Topology Service - Service responsible for locating and querying the Global Catalog and Domain Controller servers.

Routing Tables - A map of the topology used by the routing component to make routing decisions.

DNS - Exchange 2010 uses both a standard and enhanced DNS client to perform next hop name resolution. Enhanced DNS supports load-balancing for transport server roles.

SMTP - Protocol used for communications between transport server roles

RPC - Remote Procedure Calls are used by hub transport servers to submit mail to Mailbox Server roles within the same active directory site.

I strongly encourage you to check out the Microsoft TechNet articles under Understanding Transport for further details.

While much of the transport architecture was developed for Exchange 2007 there are some new and improved features. In the Toolbox you will now find the Routing Log Viewer. A feature that I think will be very popular for messaging compliance is the new Moderated Transport with will force approval by moderators for selected email messages.

-Rich Luckett

Related Courses

Configuring, Managing, and Troubleshooting Microsoft Exchange Server 2010 (M10135)

Designing and Deploying Messaging Solutions with Microsoft Exchange Server 2010 (M10233)

Author: Richard Luckett