You are the messaging engineer for your company. Your company has a main office and five branch offices.
Each office has three Exchange Server 2007 servers. Two Mailbox servers are configured as a single copy cluster. The third server is configured a Hub Transport server.
During a recent Hub Transport server failure, some Microsoft Office Outlook users reported that they were unable to send or receive messages.
You need to design an Exchange organization that meets the following requirements:
Ensure that the failure of a Hub Transport server on the network does not prevent message delivery.
Load balance the delivery of messages between multiple Hub Transport servers in each office.
What should you do?
A.
Install an additional Hub Transport server in each office.
B.
Install the Windows Clustering service on all Hub Transport servers.
C.
Create a new Send connector on all Hub Transport servers.
D.
Create a CNAME record for each Hub Transport server and use round robin DNS.
Explanation:
Each Mailbox server maintains a list of the Hub servers also located in its AD site.To keep this submission server list up-to-date, the server discovery mechanism repeats every ten minutes.
When a message is ready for retrieval from a senders mailbox, the Mail Submission Service notifies one of the Hub servers on this list. If the Mailbox server also runs the Hub role, this same machine it notified first. Otherwise, by default, the Submission Service uses round robin to load balance notification events across all the Hub servers in the local site. If the first Hub server cant be contacted, its marked as inactive and the Submission Service fails over to the next server on the list. This way, each active Hub server processes an equal share of messages.
http://technet.microsoft.com/en-us/library/bb232193.aspx
Load balancing applies to all types of outgoing mail connectors on both Edge and Hub servers — SMTP, Routing Group, Foreign. If multiple source servers from one AD site are configured on such a connector, load balancing is achieved by distributing links across all these servers in a round robin fashion. However, load balancing doesnt take place if the machine relaying the mail is itself configured as a source server for that particular connector. In this case, local server proximity takes precedence over local AD site proximity, and the mail is always routed by this same computer.
http://technet.microsoft.com/en-us/library/bb267003.aspx