Okay. Two Forests, Two Domains
Exchange 2007 -> exch2007.com
Exchange 2013 -> exch2013.com
Exchange Server 2007 is SP3 CU14 Standard and is running on Server 2k3 x64 R2 SP2
Exchange Server 2013 is SP1 CU7 Enterprise and is running on Server 2k12 x64 R2 Standard.
I've purchased Take Two's migration software, attempted to install it on the Exchange 2007 box, but it gave me this error when I attempted to validate the source server: Failed to open mailbox 'Mailbox - UserName'.
When I attempted to validate the Target Server it gives me an error regarding impersonation permissions, and the exchange server doesn't support the requested version.
However, I installed the same software on a Windows 7 x64 Machine that is in the old domain and it connects and synchronizes between to two, but it is unbelievably slow ~.3 MB per min. (600GB total transfer to complete).
I've tried to discern instructions on how to use 2007/2013 EAC to move mailboxes. But I am way out of league for this.