Export Folders as MBOX Files Using a Script
Archive Message Folders by Jolly Roger
  
  This script archives each folder in your Entourage folder list to a folder on your desktop named "Entourage Archives".
      The script preserves the hierarchy of the folders, as they exist in the Entourage folders list, by creating sub-folders in the "Entourage Archives" folder that correspond to the sub-folders in Entourage.
      The exported MBOX files have the same name as the folders in Entourage, with the exception that forward slash characters (/) are replaced with dash characters (-) to avoid problems with the Mac OS X file system.


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  Export Folders by Barry Wainwright
  
  You must create the archive folder yourself before running the script.
      All folders and subfolders are dumped into one folder. This requires you to have unique names so you can maintain the folder order.


Source