As this previous page in the Recycle Bin instructions notes:
You can use Active Directory Recycle Bin to restore all deleted objects that were previously stored in AD DS. However, if you use Active Directory Recycle Bin to restore deleted Group Policy objects (GPOs) or Exchange-related objects that were previously stored in AD DS, any application-specific data for these objects that was not stored in AD DS will not be restored.
Since the relationship between a mailbox and a user is defined by the ownership information on the mailbox (ie. information stored in Exchange), The Active Directory Recycle Bin does not restore this relationship.
When a user is deleted in Active Directory, the mailbox will be marked as disonnected before being removed completely, look into reconnecting the mailbox instead of hammering your head against Active Directory: http://technet.microsoft.com/en-us/library/bb123490(v=exchg.141).aspx