Postbox has a profile manager which can be used to manage multiple profiles. This shouldn't be confused with the ability to support multiple accounts which you can do within a single profile.

The profile manger allows you to switch between profiles in addition to creating and deleting profiles.

Accessing the Profile Manager

Make sure Postbox is not already running.

Windows

From the Windows "Start" menu, choose "Run" (this is "Start Search" on Windows Vista") then type in the following:

postbox.exe  -ProfileManager

Mac OS X

Launch Terminal on the Mac - Applications / Utilities / Terminal and then type in:

/Applications/Postbox.app/Contents/MacOS/postbox-bin -profilemanager