diff --git a/modoboa/core/commands/postfix_maps.py b/modoboa/core/commands/postfix_maps.py
index eda26f4fc..021ceae9b 100644
--- a/modoboa/core/commands/postfix_maps.py
+++ b/modoboa/core/commands/postfix_maps.py
@@ -2,6 +2,8 @@
 import getpass
 import inspect
 import os
+import sys
+import datetime
 from django.template import Context, Template
 from . import Command
 
@@ -46,6 +48,12 @@ query = {{ query|safe }}
                              query=getattr(v, args.dbtype)))
             )
             with open("%s/%s" % (args.destdir, v.filename), "w") as fp:
+                print >> fp, """# This file was generated on %s by running:
+# %s %s
+# DO NOT EDIT!
+""" % (datetime.datetime.now().isoformat(),
+       os.path.basename(sys.argv[0]),
+       ' '.join(sys.argv[1:]))
                 print >> fp, content
 
 
diff --git a/modoboa/extensions/amavis/views.py b/modoboa/extensions/amavis/views.py
index f1973b966..ba89903ee 100644
--- a/modoboa/extensions/amavis/views.py
+++ b/modoboa/extensions/amavis/views.py
@@ -1,16 +1,15 @@
 # coding: utf-8
 import email
 from django.shortcuts import render
-from django.http import HttpResponseRedirect, HttpResponse, Http404
+from django.http import HttpResponseRedirect, Http404
 from django.template import Template, Context
-from django.utils import simplejson
 from django.utils.translation import ugettext as _, ungettext
 from django.core.urlresolvers import reverse
 from django.contrib.auth.decorators \
     import login_required, user_passes_test
 from django.db.models import Q
 from modoboa.lib import parameters
-from modoboa.lib.exceptions import ModoboaException, BadRequest
+from modoboa.lib.exceptions import BadRequest
 from modoboa.lib.webutils import (
     getctx, ajax_response, render_to_json_response
 )
@@ -49,7 +48,7 @@ def empty_quarantine(request):
     content = "<div class='alert alert-info'>%s</div>" % _("Empty quarantine")
     ctx = getctx("ok", level=2, listing=content, navbar="",
                  menu=quar_menu(request.user))
-    return HttpResponse(simplejson.dumps(ctx), mimetype="application/json")
+    return render_to_json_response(ctx)
 
 
 @login_required
@@ -107,7 +106,7 @@ def _listing(request):
     navbar = lst.render_navbar(page, "listing/?")
     ctx = getctx("ok", listing=content, navbar=navbar,
                  menu=quar_menu(request.user))
-    return HttpResponse(simplejson.dumps(ctx), mimetype="application/json")
+    return render_to_json_response(ctx)
 
 
 @login_required
@@ -178,7 +177,7 @@ def viewmail(request, mail_id):
 """).render(Context({"url": reverse(getmailcontent, args=[mail_id])}))
     menu = viewm_menu(request.user, mail_id, rcpt)
     ctx = getctx("ok", menu=menu, listing=content)
-    return HttpResponse(simplejson.dumps(ctx), mimetype="application/json")
+    return render_to_json_response(ctx)
 
 
 @login_required
diff --git a/modoboa/lib/webutils.py b/modoboa/lib/webutils.py
index b2da344a8..843897378 100644
--- a/modoboa/lib/webutils.py
+++ b/modoboa/lib/webutils.py
@@ -5,12 +5,12 @@ This module contains extra functions/shortcuts used to render HTML.
 """
 import sys
 import re
+import json
 from django.http import HttpResponse, HttpResponseRedirect
 from django.contrib.auth.decorators import login_required
 from django.shortcuts import render_to_response
 from django.template.loader import render_to_string
 from django import template
-from django.utils import simplejson
 from django.conf import settings
 
 
@@ -86,7 +86,7 @@ def ajax_response(request, status="ok", respmsg=None,
     if url is not None:
         jsonctx["url"] = url
     jsonctx["norefresh"] = norefresh
-    return HttpResponse(simplejson.dumps(jsonctx), mimetype="application/json")
+    return HttpResponse(json.dumps(jsonctx), mimetype="application/json")
 
 
 def render_to_json_response(context, **response_kwargs):
@@ -95,7 +95,7 @@ def render_to_json_response(context, **response_kwargs):
     :param dict context: response content
     :return: ``HttpResponse`` object
     """
-    data = simplejson.dumps(context)
+    data = json.dumps(context)
     response_kwargs['content_type'] = 'application/json'
     return HttpResponse(data, **response_kwargs)