To bounce a message using the conversion channel set OVERRIDE-OPTION-FILE=1 in the appropriate conversions file entry and add the following line to your conversion script:
echo "STATUS=178029946" >> $OUTPUT_OPTIONS
If you wish to add a short text string to the bounced message add the following line to the conversion script:
echo OUTPUT_DIAGNOSTIC=text-string >> $OUTPUT_OPTIONS
where text string is something like: “The message sent from your machine contained a virus which has been removed. Be careful about executing email attachments.”