The default import files used by directory access functions are comma-separated value (.CSV) files that can be read and written with Microsoft Excel. You can use the second column in the .CSV file to state the mode of the operation: Update, Create, Delete, or Modify. For more information, see the Microsoft Exchange Server Administrator's Guide and Specifying the Import Mode for BatchImport.
The DIRSYNC sample application demonstrates how a completely different file format can be implemented using the directory access functions of the Microsoft Exchange Server SDK. The format is described in DIRSYNC: Importing and Exporting Mailboxes.