One of the main limitations of Microsoft Outlook is that it is not possible to run multiple Outlook instances that connect to different Microsoft Exchange Servers. It is possible to run multiple Outlook profiles on the same computer system but it is not possible to connect to different Exchange Servers.

Enter Extra Outlook, a lightweight freeware software application that makes it possible to run multiple Outlook instances on the same computer system. You can find a detailed explanation of the workings of that application at the REblog. A general description would be that Extra Outlook will intercept Outlooks exit process when starting a second instance of the email client which allows the user to select a different profile (and thus Exchange Server) during startup.

Extra Outlook is a command line tool:

ExtraOutlook.exe "C:\Program Files\Microsoft Office\Office12\OUTLOOK.EXE"

You can also create shortcuts on the desktop that make use of this program to launch additional Outlook instances comfortably. Extra Outlook is compatible with Microsoft Outlook 2003 and Microsoft Outlook 2007.