fml accepts control commands which is sent as a mail. It is called "command mail". The use of CUI (makefml/fml) is basic in fml world. Consider elena ML. Send the command mail to elena-ctl@fml.org which is the address for command mail. MTA receives the mail and finally kicks off /usr/local/libexec/fml/command program. This program receives the mail (command mail) from STDIN , processes the requests and sends back the result to the sender. The mail to send back is passed to MTA for delivery via SMTP. The result is aggreagated to one msssage as MIME/Multipart . This is different from &fml4; behaviour. All modules which CUI, GUI and command mail uses are implented as FML::Command:: class.