MS Exchange Packaging
MS Exchange is an ideal Messaging Platform for Companies with as low as 5 PC’s to Enterprises having thousands of PC’s. Depending upon the size of the Company, the right MS Exchange packaging is available.
1) For Companies having 5 to 75 PC’s 
The best way for Companies having less than 75 PC’s to buy MS Exchange is to purchase Windows Small Business Server(SBS) 2008 standard or premium. When Customers buy SBS, they get MS Exchange tightly integrated with Windows Server 2008. For more details on Windows Small Business Server , please click on the link below:
http://www.microsoft.com/sbs/en/us/default.aspx
To understand how Fast Growing Business can use this Solution please refer to the following Solution on Microsoft website:
Technology Solution for Fast Growing Small Business
2) For Companies having more than 75 PC’s 
If a Company has more than 75 PC’s, then they should purchase MS Exchange as a standalone product. The MS Exchange standalone version is available as Standard and Enterprise editions. If Companies have a need for high availability clustering, then the Enterprise edition is the version of choice. For more details on MS Exchange Server standalone product, please click the link below:
http://www.microsoft.com/exchange/default.mspx
3) BPOS
Microsoft Online Services gives your business the powerful productivity capabilities; all hosted at Microsoft Datacenters. Microsoft Online Services makes it easy for you to leverage and rapidly deploy familiar Microsoft server products as flexible services.
To understand the BPOS in details please refer to BPOS features
To understand the benefits of Cloud Computing, please refer to Cloud Computing .
Please find the details of the service at :
http://www.microsoft.com/online/exchange-online.mspx
To understand how Business can benefit from Hosted Solution, please refer to the following Solution on Microsoft website:
Cloud Computing based Unified Messaging Solution for Fast Growing Business