Great post from MSExchange Team about namespace planning in Exchange Server 2013.
A while back we promised an article on namespace planning and load balancing principles with Exchange 2013. We’re finally going to fulfill that promise as a series of articles. The articles will span several topics, including namespace planning, load balancing, client connectivity coexistence, and certificate planning. As the title suggests, this first article will cover namespace planning principles.
Read more at source: http://blogs.technet.com/b/exchange/archive/2014/02/28/namespace-planning-in-exchange-2013.aspx