vvrpgsporcupineorg ralf hildebrandt docs read postfix 23x supports milter protocol 8 3 4 postfix 25x supports milter protocol 8 6 milter_readme says default version 2 protocol versions 3 4 postfix 23 later 6 postfix 25 later report features added removed report gazillion features releases common wheres difference anyway protocol version number sent initial postfixtomilter handshake introduces new features milter api documentation sits sendmail source code tree reproduced postfix avoid interoperability problems postfix announce support features exist configured protocol version wietse thu 07 aug 2008 221024 0500 milter version clarification