The different Exchange organizations were installed using the default or the same naming conventions for the Organization Name and the Site Name, and the same user account / mailbox name was also used for the mailbox. So the legacyExchangeDN attribute for the mailbox would be exactly the same, for example:
/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=mailbox
For existing users who have the same User Account/Mailbox name, you can create a new mailbox with a different name and use the ExMerge utility (for Exchange 2003 or earlier) or the Export-Mailbox and Import-Mailbox powershell cmdlets (for Exchange 2007 or later) to move that user’s items to the new mailbox.
ExMerge can be found here:
Instructions for use of the Export-Mailbox and Import-Mailbox commands can be found here:
Article ID: 2296089 - Last Review: 04/25/2013 21:05:00 - Revision: 3.0