Description

   If you do not specify an input file, the MAIL$MAILFILE_INFO_FILE
   returns information about the currently open mail file.

   Folder Action Routines

   If you use the item code MAIL$_MAILFILE_FOLDER_ROUTINE to specify
   a folder name routine, MAIL$MAILFILE_INFO_FILE passes control
   to a user-specified routine. For example, the folder action
   routine could display folder names. The user routine must return
   a 32-bit integer code. If the return code indicates success, the
   interaction between the user's routine and the callable routine
   can continue.

   The folder action routine passes a pointer to the descriptor of
   a folder name as well as the user data longword. A descriptor of
   zero length indicates that the MAIL$MAILFILE_INFO_FILE routine
   has displayed all folder names. If you do not specify the item
   code MAIL$_MAILFILE_FOLDER_ROUTINE, MAIL$MAILFILE_INFO_FILE does
   not call any folder action routines.