/FDL=filename

    Specifies a File Descriptor Language (FDL) definition file to use
    when converting the specified attachment into an output file. Use
    this qualifier when the desired file characteristics differ than
    those produced by the MIME utility default settings, or are different
    than those specified in the MIME$MAILCAP.DAT file

    Note that the /FDL qualifier will override the default FDL file
    specified in MIME$MAILCAP.DAT file (if one exists).

    FDL files can be created with the ANALYZE/RMS/FDL command and also
    created and edited with the EDIT/FDL command.