As you may already know, current BPOS customers are currently in the process to be migrated to the new Microsoft Online Service called Office 365
To assist customers and partners in this migration/transition, Microsoft has published a BPOS Transition Center web site.
You can go to http://www.microsoft.com/online/transition-center_before.aspx to learn more about the transition, the actions to be done before, during and after the migration process
Enjoy (and good luck, as a migration is always something very sensitive – even if in this case the migration itself is done by Microsoft Online Services)