Exchange Server 2013 can be deployed only in an environment where there has never before been an Exchange Server deployment. This is because Exchange 2013 doesn't coexist with Exchange 2010. This behavior will be corrected in an upcoming service pack for Exchange 2010. But at the moment, if you deploy 2013, then you must deploy only 2013, and only where there are no coexistence concerns. This pretty much rules out an immediate deployment of Exchange 2013 for the vast majority of businesses.
As of this writing, Microsoft has promised that the service pack allowing for interoperability between Exchange 2013 and earlier versions will be released sometime before the end of March. But this begs the question: Why release a product when you know almost none of your customers can use it without supporting software that will not be ready for several months still?
Keeping the services of Exchange running at peak performance can be particularly challenging. For example, Microsoft has discontinued the Exchange Best Practices Analyzer, which was a tool you could run on your deployments that would compare the state of your installation to known-good attributes of successful deployments and highlight the differences. It also provided practical advice and guidance about rectifying the deficiencies.
There is no equivalent for Exchange 2013.
Also gone are the Exchange Mail Flow Troubleshooter, which was great for determining why messages might not be showing up when you knew they were sent; the Exchange Performance Troubleshooter; and the Exchange Routing Log Viewer. No replacements for these tools have been announced.
There is no support for BlackBerry Enterprise Server (BES) to communicate with Exchange Server 2013. The CDO/MAPI download is not yet available for Exchange 2013 and is "likely the primary reason" BES support is not yet available, says Smith. This download, provided by Microsoft, is the interface that BlackBerry services use to access Exchange, view and compose messaging, and access the transport layers to route messages appropriately.
Unless you are using a third-party solution that rides on top of ActiveSync, or you are using ActiveSync itself, you are probably using BlackBerry, which means your mobile phone users will not have messaging until these bits are released.
There is no current guidance on when this download will be available. The new BlackBerry 10 products generally use ActiveSync or BlackBerry Mobile Fusion, the new server product from BlackBerry (formerly Research in Motion), both of which will work with Exchange 2013. However, any older BlackBerry device still requires the MAPI download and there are millions of those devices in use around the world. Another point in the "no go" column.