The EHLO blog posted an important announcement today regarding Exchange 2010 in hosted environments. Previously, for Microsoft to support your multi-tenant deployment of Exchange 2010, you had to build a whole new forest and use a special setup.com /hosting installation process. There were other significant limitations as well.
The strict support statement, combined with Microsoft’s release of Office 365 really came as a one-two punch to some of the smaller companies who wished to host Exchange but could not afford to employ developers and/or take the risk of forfeiting support from Microsoft. It seemed like Microsoft may have lost some love for their hosting partners.
With the Exchange 2010 SP2 update (scheduled to launch later this year), you will be able to host a multi-tenant environment with a regular deployment of Exchange. This is made possible by the new Address Book Policies and specific configurations to be documented with the SP2 release.
Personally, I’d look at this very carefully before deploying any new /hosting environments. This (SP2) seems like a much simpler deployment to maintain.