The ALST (Address List Segregation Tool) allow for Exchange 2007 SP 1 and above environments to be split into seperate companies.
Address list segregation is a process where Exchange admins can segment their users into separate groups and implement security policies so that groups of users can see only their specific address list, therefore creating "virtual organisations".
- .NET – version 3.5 of the Framework
- Requires Powershell 2.0, Exchange Management Tools and the Quest AD Cmdlets to be installed on the Segregation Machine (the tool does not support Powershell 1.0)
- x64 versions of Windows 2003, 2008 (including R2) and Exchange 2007 SP1 – 3
Please see the following article