NAME
       CannotExport -- Mark a message as not being exportable.

   SYNOPSIS
       CannotExport( login, msgNum, error )
                      D2      D3     D4

       VOID CannotExport( LONG, LONG, STRPTR );

   FUNCTION
         Tell  the  MBP  that  you cannot export this message, due to any
       reason.   The MBP will then look if other exporters still could be
       able to export the message or do some error processing otherwise.
         It may use the supplied error-string therein.  This error-string
       should  be  a  short  description  why  the  message  could not be
       exported.  By convention it should not be longer than 80 bytes.

   INPUTS
       msgNum - Number of the message.
       error  - Short string (<80 chars).

   NOTES
         This function may only be called by exporters.
         See also  ExportedMsg().

   BUGS
         The  MBP currently does not write a bounce mail to the author of
       the mail, but sets a special global bit instead, which would allow
       a 'bounce daemon' to automatically write bounce mails.

   SEE ALSO
        ExportedMsg()