Microsoft Solution for Hosted Messaging and Collaboration 4.5 has been released !

HMC 4.5 brings together powerful Microsoft enterprise products such as
Microsoft Exchange Server, Microsoft Windows SharePoint Services, and
now gives you Microsoft Office Communications Server 2007, which
manages all real-time communications such as instant messaging (IM)
and audio and video conferencing.

Other new features and enhancements:

• Exchange Server 2007 SP1:  Web-based OABs and resource mailboxes
• Windows SharePoint Services:  multi-tenant People Picker functionality
• Provisioning capabilities have been expanded:
• Microsoft Provisioning System (MPS)
  cross data store integration procedures
• Individual Information Worker (IIW) tenant model
• New SDK, updated for HMC 4.5

Get started now with HMC 4.5 and HMC 4.5 SDK