With the recent releases of Exchange Server 2013 RTM CU1, Exchange 2013 sizing guidance, Exchange 2013 Server Role Requirements Calculator, and the updated Exchange 2013 Deployment Asistant, on-premises customers now have the tools you need to begin designing and performing migrations to Exchange Server 2013. Many of you have introduced Exchange 2013 RTM CU1 into your test environments alongside Exchange 2010 SP3 and/or Exchange 2007 SP3 RU10, and are readying yourselves for the production migrations.
There's one particular Exchange 2010 design choice some customers made that could throw a monkey wrench into your upgrade plans to Exchange 2013, and we want to walk you through how to mitigate it so you can move forward. If you're still in the design or deployment phase of Exchange Server 2010, we recommend you continue reading this article so you can make some intelligent design choices which will benefit you when you migrate to Exchange 2013 or later.
Read more at source: http://blogs.technet.com/b/exchange/archive/2013/05/23/ambiguous-urls-and-their-effect-on-exchange-2010-to-exchange-2013-migrations.aspx