The CNBUILD utility compiles the textual configuration, option,
    mapping, security, conversion, system wide filter, and alias
    files into a single OpenVMS shareable image. The resulting image,
    PMDF_CONFIG_DATA (usually PMDF_EXE:CONFIG_DATA.EXE), can then be
    installed with the OpenVMS INSTALL utility.

    Whenever a component of PMDF (e.g., a channel program) must read
    any possibly compiled configuration component, it first checks
    to see if the PMDF_CONFIG_DATA image exists. If it does, the
    image is merged into the running program using the OpenVMS RTL
    routine LIB$FIND_IMAGE_SYMBOL. There are five exceptions to this
    rule. The first is CNBUILD itself, which for obvious reasons
    always reads the text files and never tries to load the image
    form of the configuration data. The remaining four exceptions are
    TEST/REWRITE, TEST/MAPPING, TEST/FAX_ROUTING, and TEST/X400 which
    can all be instructed with the /NOIMAGE_FILE qualifier to ignore
    any compiled image information. This facility in TEST/REWRITE is
    useful for testing changes prior to compiling them.

    The reason for compiling configuration information is simple:
    performance. The only penalty paid for compilation is the need
    to rebuild and reinstall the file any time the configuration or
    alias files are edited. Also, be sure to restart any channels or
    components which load the configuration data only once when they
    start up (e.g., the PMDF multithreaded TCP SMTP server, the POP
    or IMAP servers, FAX_RECEIVE, BITNET channels, or, if using PMDF-
    MR for MR TS replacement, the All-in-1 Sender, All-in-1 Fetcher,
    and MailWorks server).

    Once you begin to use a compiled configuration, it will be
    necessary to recompile the configuration every time changes are
    made to any of the following files: the PMDF configuration file,
    PMDF.CNF (or any files referenced by it); the system alias file,
    ALIASES.; the system mapping file, MAPPINGS.; the PMDF option
    file, OPTION.DAT; the conversions file, CONVERSIONS., the system
    wide filter file, PMDF.FILTER, the circuit check configuration
    file, CIRCUITCHECK.CNF, or the security configuration file,
    SECURITY.CNF. Until such time that the configuration is
    recompiled and reinstalled, changes to any of these files will
    not be visible to the running PMDF system.

    See the PMDF System Manager's Guide for further details on the
    use of compiled configurations.