diff --git a/common/t-mbox-util.c b/common/t-mbox-util.c
index fb1ac12e0..e9cf41215 100644
--- a/common/t-mbox-util.c
+++ b/common/t-mbox-util.c
@@ -1,156 +1,246 @@
 /* t-mbox-util.c - Module test for mbox-util.c
  * Copyright (C) 2015 Werner Koch
  *
  * This file is part of GnuPG.
  *
  * GnuPG is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 3 of the License, or
  * (at your option) any later version.
  *
  * GnuPG is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, see <https://www.gnu.org/licenses/>.
  */
 
 #include <config.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include "util.h"
 #include "mbox-util.h"
 
+#define PGM "t-mbox-util"
+
+
 #define pass()  do { ; } while(0)
 #define fail(a)  do { fprintf (stderr, "%s:%d: test %d failed\n",\
                                __FILE__,__LINE__, (a));          \
                        exit (1);                                 \
                     } while(0)
 
 
+static int verbose;
+static int debug;
+
+
 static void
 run_mbox_test (void)
 {
   static struct
   {
     const char *userid;
     const char *mbox;
   } testtbl[] =
     {
       { "Werner Koch <wk@gnupg.org>", "wk@gnupg.org" },
       { "<wk@gnupg.org>", "wk@gnupg.org" },
       { "wk@gnupg.org", "wk@gnupg.org" },
       { "wk@gnupg.org ", NULL },
       { " wk@gnupg.org", NULL },
       { "Werner Koch (test) <wk@gnupg.org>", "wk@gnupg.org" },
       { "Werner Koch <wk@gnupg.org> (test)", "wk@gnupg.org" },
       { "Werner Koch <wk@gnupg.org (test)", NULL },
       { "Werner Koch <wk@gnupg.org >", NULL },
       { "Werner Koch <wk@gnupg.org", NULL },
       { "", NULL },
       { "@", NULL },
       { "bar <>", NULL },
       { "<foo@example.org>", "foo@example.org" },
       { "<foo.@example.org>", "foo.@example.org" },
       { "<.foo.@example.org>", ".foo.@example.org" },
       { "<foo..@example.org>", "foo..@example.org" },
       { "<foo..bar@example.org>", "foo..bar@example.org" },
       { "<foo@example.org.>", NULL },
       { "<foo@example..org>", NULL },
       { "<foo@.>", NULL },
       { "<@example.org>", NULL },
       { "<foo@@example.org>", NULL },
       { "<@foo@example.org>", NULL },
       { "<foo@example.org> ()", "foo@example.org" },
       { "<fo()o@example.org> ()", "fo()o@example.org" },
       { "<fo()o@example.org> ()", "fo()o@example.org" },
       { "fo()o@example.org", NULL},
       { "Mr. Foo <foo@example.org><bar@example.net>", "foo@example.org"},
       { NULL, NULL }
     };
   int idx;
 
   for (idx=0; testtbl[idx].userid; idx++)
     {
       char *mbox = mailbox_from_userid (testtbl[idx].userid);
 
       if (!testtbl[idx].mbox)
         {
           if (mbox)
             fail (idx);
         }
       else if (!mbox)
         fail (idx);
       else if (strcmp (mbox, testtbl[idx].mbox))
         fail (idx);
 
       xfree (mbox);
     }
 }
 
 
 static void
 run_dns_test (void)
 {
   static struct
   {
     const char *name;
     int valid;
   } testtbl[] =
     {
       { "", 0 },
       { ".", 0 },
       { "-", 0 },
       { "a", 1 },
       { "ab", 1 },
       { "a.b", 1 },
       { "a.b.", 1 },
       { ".a.b.", 0 },
       { ".a.b", 0 },
       { "-a.b", 0 },
       { "a-.b", 0 },
       { "a.-b", 0 },
       { "a.b-", 0 },
       { "a.b-.", 0 },
       { "a..b", 0 },
       { "ab.c", 1 },
       { "a-b.c", 1 },
       { "a-b-.c", 0 },
       { "-a-b.c", 0 },
       { "example.org", 1 },
       { "x.example.org", 1 },
       { "xy.example.org", 1 },
       { "Xy.example.org", 1 },
       { "-Xy.example.org", 0 },
       { "Xy.example-.org", 0 },
       { "foo.example.org..", 0 },
       { "foo.example.org.", 1 },
       { ".foo.example.org.", 0 },
       { "..foo.example.org.", 0 },
       { NULL, 0 }
     };
   int idx;
 
   for (idx=0; testtbl[idx].name; idx++)
     {
       if (is_valid_domain_name (testtbl[idx].name) != testtbl[idx].valid)
         fail (idx);
     }
 }
 
 
+static void
+run_filter (void)
+{
+  char buf[4096];
+  int c;
+  char *p, *mbox;
+  unsigned int count1 = 0;
+  unsigned int count2 = 0;
+
+  while (fgets (buf, sizeof buf, stdin))
+    {
+      p = strchr (buf, '\n');
+      if (p)
+        *p = 0;
+      else
+        {
+          /* Skip to the end of the line.  */
+          while ((c = getc (stdin)) != EOF && c != '\n')
+            ;
+        }
+      count1++;
+      trim_spaces (buf);
+      mbox = mailbox_from_userid (buf);
+      if (mbox)
+        {
+          printf ("%s\n", mbox);
+          xfree (mbox);
+          count2++;
+        }
+    }
+  if (verbose)
+    fprintf (stderr, PGM ": lines=%u mboxes=%u\n", count1, count2);
+}
+
+
 int
 main (int argc, char **argv)
 {
-  (void)argc;
-  (void)argv;
+  int last_argc = -1;
+  int opt_filter = 0;
 
-  run_mbox_test ();
-  run_dns_test ();
+  if (argc)
+    { argc--; argv++; }
+  while (argc && last_argc != argc )
+    {
+      last_argc = argc;
+      if (!strcmp (*argv, "--"))
+        {
+          argc--; argv++;
+          break;
+        }
+      else if (!strcmp (*argv, "--help"))
+        {
+          fputs ("usage: " PGM " [FILE]\n"
+                 "Options:\n"
+                 "  --verbose         Print timings etc.\n"
+                 "  --debug           Flyswatter\n"
+                 "  --filter          Filter mboxes from input lines\n"
+                 , stdout);
+          exit (0);
+        }
+      else if (!strcmp (*argv, "--verbose"))
+        {
+          verbose++;
+          argc--; argv++;
+        }
+      else if (!strcmp (*argv, "--debug"))
+        {
+          verbose += 2;
+          debug++;
+          argc--; argv++;
+        }
+      else if (!strcmp (*argv, "--filter"))
+        {
+          opt_filter = 1;
+          argc--; argv++;
+        }
+      else if (!strncmp (*argv, "--", 2))
+        {
+          fprintf (stderr, PGM ": unknown option '%s'\n", *argv);
+          exit (1);
+        }
+    }
+
+  if (opt_filter)
+    run_filter ();
+  else
+    {
+      run_mbox_test ();
+      run_dns_test ();
+    }
 
   return 0;
 }