I am trying to write a script that would directly communicate to the dkim-filter process through its socket using the milter protocol. My script would essentially act like sendmail. In the process I am finding some responses whose meaning I am not aware of. For example I get responses with command 's', 'i' which don't seem to be documented as a part of milter protocol. Is there a place where I can find the meaning of these response commands from dkim-milter?