VMS Help MAIL Routines, MAIL$MAILFILE_CLOSE, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If you specify the input item code MAIL$_MAILFILE_FULL_CLOSE,
    this procedure purges the wastebasket folder automatically
    before it closes the file. If the number of bytes deleted by this
    procedure exceeds the deleted byte threshold, the system performs
    a convert/reclaim operation on the file.