At Microsoft we have challenges around messaging protection just like other organisations. But unlike other organizations we are the target of many more advanced attacks from outside the company. So our internal IT department was looking for a solution to help with this increasing problem. Exchange Server 2007 has been deployed since 2006 and marks the last major upgrade to a traditional messaging infrastructure. The diagram below shows what this looks like using Hub transfer servers in our corporate forest and Edge transport servers in our Extranet.
So we are constantly looking to stay ahead of the bad guys and moving to Exchange Hosted Services was a step in that direction. The diagram below shows this a more simple approach with all the necessary protection happening in the cloud using the hosted service.