I had a great question today:

I have three Hub Transport Servers,and one Mailbox Server, and I want   Hub Transport servers one and two used for load balanced mail delivery. Hub Transport Server three should never be used, except for mail relaying.

Obviously one of the design features of Exchange 2010 is the ability for transport load to auto-load balance, once more than one Hub Transport server is introduced. How do you take one or more of the Hub Transport Servers out of selection, without moving the affected Hub Transport server to it’s own AD site?

The Mailbox Server hosts the Mail-Submission Service, which notifies a Selected Hub Transport server than new mail is available for delivery. As such the mailbox server object holds an attribute called “SubmissionServerOverrideList”. SubmissionServerOverrideList allows you to specify which Hub Transport servers a mailbox server may use to route mail.

an Example of this may be:

Set-MailboxServer –Identity MailServer.domain.com –SubmissionServerOverrideList Hub_one.domain.com, Hub_two.domain.com

This works equally well on Exchange 2007 and Exchange 2010. ONE TINY CAVEAT THOUGH: Set-MailboxServer does not check if you’re populating SubmissionServerOverrideList with a valid hub-transport server, only if you’re specifying a valid Exchange server.