diff -upk.orig postfix-2.2.4.orig/src/global/mail_params.c postfix-2.2.4/src/global/mail_params.c
--- postfix-2.2.4.orig/src/global/mail_params.c	2005-06-23 12:47:30 +0000
+++ postfix-2.2.4/src/global/mail_params.c	2005-06-23 12:49:30 +0000
@@ -28,6 +28,7 @@
 /*	char	*var_daemon_dir;
 /*	char	*var_command_dir;
 /*	char	*var_queue_dir;
+/*	int     var_local_minimum_uid;
 /*	int	var_use_limit;
 /*	int	var_idle_limit;
 /*	int	var_event_drain;
@@ -190,6 +191,7 @@ char   *var_config_dir;
 char   *var_daemon_dir;
 char   *var_command_dir;
 char   *var_queue_dir;
+int     var_local_minimum_uid;
 int     var_use_limit;
 int     var_event_drain;
 int     var_idle_limit;
@@ -538,6 +540,7 @@ void    mail_params_init()
 	0,
     };
     static CONFIG_INT_TABLE other_int_defaults[] = {
+	VAR_LOCAL_MINUID, DEF_LOCAL_MINUID, &var_local_minimum_uid, 0, 0,
 	VAR_MAX_USE, DEF_MAX_USE, &var_use_limit, 1, 0,
 	VAR_DONT_REMOVE, DEF_DONT_REMOVE, &var_dont_remove, 0, 0,
 	VAR_LINE_LIMIT, DEF_LINE_LIMIT, &var_line_limit, 512, 0,
diff -upk.orig postfix-2.2.4.orig/src/global/mail_params.h postfix-2.2.4/src/global/mail_params.h
--- postfix-2.2.4.orig/src/global/mail_params.h	2005-06-23 12:37:33 +0000
+++ postfix-2.2.4/src/global/mail_params.h	2005-06-23 12:49:30 +0000
@@ -455,6 +455,10 @@ extern char *var_alias_db_map;
 #define DEF_LUSER_RELAY		""
 extern char *var_luser_relay;
 
+#define VAR_LOCAL_MINUID	"local_minimum_uid"
+#define DEF_LOCAL_MINUID	500
+extern int var_local_minimum_uid;
+
  /*
   * Local delivery: mailbox delivery.
   */
diff -upk.orig postfix-2.2.4.orig/src/global/mypwd.c postfix-2.2.4/src/global/mypwd.c
--- postfix-2.2.4.orig/src/global/mypwd.c	2000-11-20 18:05:27 +0000
+++ postfix-2.2.4/src/global/mypwd.c	2005-02-27 00:04:57 +0000
@@ -46,6 +46,7 @@
 
 #include <sys_defs.h>
 #include <pwd.h>
+#include <errno.h>
 #include <string.h>
 #ifdef USE_PATHS_H
 #include <paths.h>
@@ -62,6 +63,8 @@
 
 #include "mypwd.h"
 
+extern int var_local_minimum_uid;
+
  /*
   * The private cache. One for lookups by name, one for lookups by uid, and
   * one for the last looked up result.
@@ -162,6 +165,10 @@ struct mypasswd *mypwnam(const char *nam
     if ((mypwd = (struct mypasswd *) htable_find(mypwcache_name, name)) == 0) {
 	if ((pwd = getpwnam(name)) == 0)
 	    return (0);
+        if ((int) pwd->pw_uid < var_local_minimum_uid) {
+           errno = ENOENT;
+           return (0);
+        }
 	mypwd = mypwenter(pwd);
     }
     last_pwd = mypwd;
diff -upk.orig postfix-2.2.4.orig/src/util/dict_unix.c postfix-2.2.4/src/util/dict_unix.c
--- postfix-2.2.4.orig/src/util/dict_unix.c	2002-12-20 00:08:49 +0000
+++ postfix-2.2.4/src/util/dict_unix.c	2005-02-27 00:04:57 +0000
@@ -54,6 +54,8 @@
 #include "dict.h"
 #include "dict_unix.h"
 
+extern int var_local_minimum_uid;
+
 /* Application-specific. */
 
 typedef struct {
@@ -81,6 +83,10 @@ static const char *dict_unix_getpwnam(DI
 	}
 	return (0);
     } else {
+        if ((int) pwd->pw_uid < var_local_minimum_uid) {
+            errno = ENOENT;
+            return (0);
+        }
 	if (buf == 0)
 	    buf = vstring_alloc(10);
 	sanity_checked = 1;