Two connectors; same cost; same number of hops to destination; message delivery will be load balanced across the two connectors?


No. If you test this scenario then you'll find that Exchange 2007 will select one of the routes and will always deliver messages across that route whenever it can.  The connector is chosen based on the connector name - whichever comes first alphanumerically will be used.  i.e. AA_Connector will always be chosen ahead of ZZ_Connector; all being equal.  The reason given is that this makes troubleshooting less complex because you take away any load balancing algorithm from the mix.  I agree that this would make troubleshooting easier but personally I would prefer load balancing and more complex troubleshooting.  After all it's easy to disable connectors temporarily or services to troubleshoot transport issues.  Load balancing in this particular scenario would make design easier in some circumstances.  For example if you are not using EdgeSync connector configuration can be complicated, particularly if you are designing for site resilience.

Fortunately there are some great articles out there on the subject:

Exchange Server 2007 routing load balancing and fault tolerance
Exchange Server 2007 Active Directory Site and Connector Selection Algorithms
Routing to External Domains
Load Balancing and Fault Tolerance for Transport Servers

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