anchor.diff:  
       environment = {
         etc = singleton
  -        { source = "/var/postfix/conf";
  +        { source = "/var/lib/postfix/conf";
             target = "postfix";
           };
   
  
positive.code:   group = cfg.group;
    setgidGroup = cfg.setgidGroup;
  
    mainCf =
      ''
        compatibility_level = 2
  
        queue_directory = /var/postfix/queue
        command_directory = ${pkgs.postfix}/sbin
        daemon_directory = ${pkgs.postfix}/libexec/postfix
  
        mail_owner = ${user}
        default_privs = nobody
  
negative.code:     services.mail.sendmailSetuidWrapper = mkIf config.services.postfix.setSendmail {
        program = "sendmail";
        source = "${pkgs.postfix}/bin/sendmail";
        group = setgidGroup;
        setuid = false;
        setgid = true;
  