Hi, i've just started to look into Exchange 2010. i've not used exchange 2007 or 2010 before but have used 2003 for some time. I've got the MS Press 70-662 book and seen this statement which i am confused by The Mailbox and Hub Transport Roles must exist in each Active Directory Site for email message to flow correctly. Should it not be the case that If you install the mailbox role in an AD site that you also need to install the HUB Transport role in the same AD site - rather than installing both in every AD site? Thanks

Correct. If you install the mailbox role, you need the HT role installed in that same AD site as well and only in those AD sites that require mailbox servers.

Thanks "AndyD" for clarifying, made me really confused as well.Regicide

Per Microsoft, you might want to add CAS in that same site as well.