When you have multiple profiles in Outlook, you can choose which one is used when you start Outlook.
Open Control Panel, search for Mail and choose Show Profiles.
If you always want to start with the same profile, choose Always use this profile.
If you want to select the profile when Outlook starts, select your most used profile in the Always use this profile menu, then change the setting to Prompt for a profile to be used.
When you start Outlook, the profile listed in the Choose Profile dialog will be selected and you'll have the option of choosing a different profile.
If you prefer to use shortcuts to open Outlook, you can create a shortcut to open Outlook using a specific profile. Use the command line switch /profile profile_name, replacing profile_name with your profile's name.
Create a shortcut to Microsoft Outlook, then add the following to the target command for the shortcut.
/profile "<profile name>"
For example, if Microsoft Outlook is installed in C:\Program Files\Microsoft Office and I want to start it with a profile named "MS Fax only," here's the command I would use in the shortcut (put it all on one line, of course):
C:\Program Files\Microsoft Office\Office10\Outlook.exe /profile "MS Fax only"
Right-click on the desktop and choose New > Shortcut then follow the wizard. Alternately, you can copy an existing Outlook shortcut and edit it, adding the /profile switch and desired profile name to the shortcut.
The profile switch also works with the Run command (use Windows key + R to open Run). Type outlook.exe /profile profile_name in the Run box then press Enter to open Outlook using that profile.
Make sure you include quotation marks around the path and profile if they contain spaces.
"C:\Program Files\Microsoft Office\Office\OUTLOOK.EXE" /profile "Personal only"
Outlook profiles are only available if you are running Outlook 97 or Outlook 2002 and newer or use Outlook 98 or Outlook 2000 in Corporate/Workgroup mode.
Outlook 2000 and Outlook 98 in Internet Mail Only mode do not utilize MAPI profiles like Corporate mode. Since IMO mode uses a static name for its one "profile," if you want to use multiple profiles, you must set up different Windows users to have unique Windows logons. Under Win9x you can enable OS level user profiles on the User Profiles tab of the Control Panel's Passwords applet. Once enabled you have log into Windows with a user name (and password - although the password can be blank).
How to tell which Microsoft Outlook profile you're using
For other command-line switches you can use when starting Outlook, read the Help topic on Control What Happens When You Start Outlook and see:
Command Lines Switches for Outlook 2010
Command Lines Switches (older versions)