anchor.diff:          description = "
             Entries for the virtual alias map.
           ";
  +      };
  +
  +      extraMasterConf = mkOption {
  +        default = "";
  +        example = "submission inet n - n - - smtpd";
  +        description = "Extra lines to append to the generated master.cf file.";
         };
   
       };
  
positive.code:     ''
      + cfg.extraConfig;
  
    aliases =
      optionalString (cfg.postmasterAlias != "") ''
        postmaster: ${cfg.postmasterAlias}
  
negative.code:   aliasesFile = pkgs.writeText "postfix-aliases" aliases;
    virtualFile = pkgs.writeText "postfix-virtual" cfg.virtual;
    mainCfFile = pkgs.writeText "postfix-main.cf" mainCf;
    masterCfFile = pkgs.writeText "postfix-master.cf" masterCf;
  
  in
  
  