Microsoft Solution for Hosted Messaging and Collaboration version 4.5 has two design points that support the theme of a single, scalable solution. There is a single reference architecture for Hosted Messaging and Collaboration version 4.5 - The design points represent "check steps" in the architecture that validate the formulas used to scale the solution.

These design points are:

• Entry Scale Tier - MAPI subscriber base from 5,000-20,000.
  
• Upper Scale Tier - MAPI subscriber base from 20,000-100,000.
  

As part of the architecture, a process that consists of scale out formulas for components and documentation to support that scale out growth can be used by service providers as their business grows.

The "Upper Scale Tier" design point represents a larger deployment and not the maximum capacity of the solution.

For more information about scaling by using Exchange Server 2007 SP1, see Scalable Hosted Exchange Architecture.