With the release of Exchange 2007 and then 2010, Microsoft moved admins to a role-based model for deployment, with changes both to roles and services that admins should understand. Exchange 2013 takes that evolution even further.
The essential roles for any Exchange deployment include Client Access, Hub Transport, and Mailbox. As the roles orientation has deepened, Microsoft has also been consolidating them. In Exchange 2013, the old Hub Transport role, which routes incoming and outgoing messages through the hub-transport server, has been incorporated in the Client Access and Mailbox roles. The Transport service that ran on the Hub Transport server has been moved to the Mailbox role.
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Exchange 2013 brings with it other services to help move mail along. On the Client Access side is the new Front-end Transport service -- essentially a proxy solution for inbound messages from the Internet to a mailbox server, though it can be configured to relay messages from the mailbox server back out to the Internet. On the mailbox server, in addition to the Transport service (which handles mail queueing), Exchange 2013 provides the Mailbox Transport Delivery service (which accepts email from the Transport services over SMTP and converts it to RBC, then delivers it to the mailbox database itself) and the Mailbox Transport Submission service (which takes mail from the mailbox database using RPC and passes it off to the Transport service using SMTP).
The removal of the Hub Transport role isn't the only change in 2013 mail flow you should understand. Another change is the use of delivery groups to determine how mail will flow and route between servers in different Active Directory sites. In Exchange 2007 and 2010, mail routing was done based on Active Directory sites and the cost of Active Directory site links, though you could adjust the costs for Exchange links to override if you wanted.
One part of the new Exchange 2013 transport improvement is the use of delivery groups, and Active Directory sites are considered simply one of the types wherein. Other types include DAGs (database availability groups) as boundaries. If a group of mailbox servers are part of a DAG but exist in different sites, the Mailbox server will not consider the Active Directory site and site-link costs when routing a message; instead, it will focus on other DAG members in the delivery group to route the message. It does so even if the mailbox server is in another site, regardless of whether another Mailbox server is outside the DAG in the same site.
Along with the Routable DAG Delivery Group and Active Directory Site Delivery Group, there are also Version Routing Delivery Groups (based on servers with the same Exchange version), Connector Source Server Delivery Groups (based on servers of different types that are coped as source servers for a send connector), and Distribution Group Expansion Server Delivery Groups (based on expansion servers for a distribution group).
Another transport change includes the use of a SafetyNet. This feature existed in Exchange 2007 and 2010 as the transport dumpster, a fail-safe mechanism to capture email that might have been lost during a failover or switchover. In Exchange 2013, this feature is taken to the next level: Messages are held in a queue database on each mailbox server, which by default holds these messages for two days. If a failover doesn't go well, the mailbox server checks the queue database of the SafetyNet for any messages that need to be restored.
For more detail on the services, ports, and architectural adjustments, there's a good TechNet article you should read. It has a couple of detailed charts illustrating how mail flow works in Exchange 2013 that really help pull these new concepts together.
This story, "Understanding Exchange 2013: New transport features," was originally published at InfoWorld.com. Read more of J. Peter Bruzzese's Enterprise Windows blog and follow the latest developments in Windows at InfoWorld.com. For the latest business technology news, follow InfoWorld.com on Twitter.