rem: msg->setHeaderField( "X-KMail-Identity", id ); return -1;
add: if ( mParameter.isEmpty() ) return ErrorButGoOn; msg->setHeaderField( "X-KMail-Transport", mParameter ); return GoOn;
context: int KMFilterActionIdentity::process(KMMessage* msg, bool& ){  msg->setHeaderField( "X-KMail-Identity", id );  return -1;}