Microsoft Exchange currently commands an impressive 33% installed base market share of the insourced messaging software market, up from 31% last year and expected to reach 39% by 2009. MS Exchange is also expected to play a bigger role in the hosted email market. Thanks to the scalability improvements and hosted licensing model of Exchange 2003, more and more service providers are choosing to use Exchange as a platform for business class email services. In terms of versions, MS Exchange 2003 is now the most widely deployed version of Exchange, according to Radicati Group. On the client side, the study states that MS Outlook accounts for about 60% all of corporate email clients in use.