diff -Naur cyrus-imapd-2.2.10.orig/lib/auth_unix.c cyrus-imapd-2.2.10/lib/auth_unix.c
--- cyrus-imapd-2.2.10.orig/lib/auth_unix.c	Tue Sep 14 00:49:29 2004
+++ cyrus-imapd-2.2.10/lib/auth_unix.c	Thu Dec 16 08:36:32 2004
@@ -48,6 +48,7 @@
 #include <stdlib.h>
 #include <pwd.h>
 #include <grp.h>
+#include <stdio.h>
 #include <ctype.h>
 #include <string.h>
 
@@ -226,6 +227,10 @@
     struct passwd *pwd;
     struct group *grp;
     char **mem;
+    FILE *groupcache;
+    char fnamebuf[1024];
+    const char *config_dir =
+        libcyrus_config_getstring(CYRUSOPT_CONFIG_DIR);
 
     identifier = auth_canonifyid(identifier, 0);
     if (!identifier) return 0;
@@ -242,8 +247,11 @@
 
     pwd = getpwnam(identifier);
 	
+    strcpy(fnamebuf, config_dir);
+    strcat(fnamebuf, "/group.cache");
+    groupcache = fopen(fnamebuf, "r");
     setgrent();
-    while ((grp = getgrent())) {
+    while (grp = ( (groupcache) ? fgetgrent(groupcache) : getgrent() )) {
 	for (mem = grp->gr_mem; *mem; mem++) {
 	    if (!strcmp(*mem, identifier)) break;
 	}
@@ -256,6 +264,7 @@
 	}
     }
     endgrent();
+    if (groupcache) fclose(groupcache);
     return newstate;
 }