We have received a few different queries through support on
how Exchange 2013 works with eDiscovery and legal hold.  Here is a great article from the office SharePoint
team that talks about eDiscovery and legal hold with the SharePoint, Exchange
and Lync 2013 products.

 

http://blogs.office.com/b/sharepoint/archive/2012/11/08/intro-to-ediscovery-in-sharepoint-exchange-and-lync-2013.aspx

 

We also have an eDiscovery FAQ that comes in handy if you
are looking for information about Microsoft office 365, SharePoint, Exchange
and Lync.

 

http://social.technet.microsoft.com/wiki/contents/articles/19485.ediscovery-faq.aspx