diff --git a/README.rst b/README.rst
index e34f4e9..ed504d3 100644
--- a/README.rst
+++ b/README.rst
@@ -8,7 +8,9 @@ An installer which deploy a complete mail server based on Modoboa.
    This tool is still in beta stage, it has been tested on Debian
    Jessie (8) only.
 
-   /tmp partitions must be mounted without ``noexec``.
+.. warning::
+      
+   ``/tmp`` partition must be mounted without the ``noexec`` option.
 
 Usage::
 
@@ -26,9 +28,11 @@ By default, the following components are installed:
 * Dovecot
 * Amavis (with SpamAssassin and ClamAV)  
 
-If you want to follow details of installation process, use --debug
+If you want more information about the installation process, add the
+``--debug`` option to your command line.
 
-At the end of the process, you should consider updating virus database with this command:: 
+At the end of the process, you should consider updating virus databases
+with this command::
 
-  freshclam
-  /etc/init.d/clamav-daemon restart
+  $ freshclam
+  $ service clamav-daemon restart
diff --git a/modoboa_installer/scripts/dovecot.py b/modoboa_installer/scripts/dovecot.py
index 9bbf8b9..3cfab68 100644
--- a/modoboa_installer/scripts/dovecot.py
+++ b/modoboa_installer/scripts/dovecot.py
@@ -2,7 +2,6 @@
 
 import glob
 import pwd
-import shutil
 
 from .. import database
 from .. import utils
@@ -64,7 +63,7 @@ class Dovecot(base.Installer):
                 self.get_file_path("fix_modoboa_postgres_schema.sql")
             )
         for f in glob.glob("{}/*".format(self.get_file_path("conf.d"))):
-            shutil.copy(f, "{}/conf.d".format(self.config_dir))
+            utils.copy_file(f, "{}/conf.d".format(self.config_dir))
 
     def restart_daemon(self):
         """Restart daemon process.
diff --git a/modoboa_installer/scripts/razor.py b/modoboa_installer/scripts/razor.py
index 91b3fcd..035b64e 100644
--- a/modoboa_installer/scripts/razor.py
+++ b/modoboa_installer/scripts/razor.py
@@ -2,7 +2,6 @@
 
 import os
 import pwd
-import shutil
 import stat
 
 from .. import utils
@@ -31,7 +30,8 @@ class Razor(base.Installer):
         path = os.path.join(self.config.get("amavis", "home_dir"), ".razor")
         utils.mkdir(path, stat.S_IRWXU, pw[2], pw[3])
         utils.exec_cmd("razor-admin -home {} -create".format(path))
-        shutil.copy(os.path.join(path, "razor-agent.conf"), self.config_dir)
+        utils.copy_file(
+            os.path.join(path, "razor-agent.conf"), self.config_dir)
         utils.exec_cmd("razor-admin -home {} -discover".format(path),
                        sudo_user=user)
         utils.exec_cmd("razor-admin -home {} -register".format(path),
diff --git a/modoboa_installer/utils.py b/modoboa_installer/utils.py
index 3ce1931..6050041 100644
--- a/modoboa_installer/utils.py
+++ b/modoboa_installer/utils.py
@@ -2,6 +2,7 @@
 
 import contextlib
 import datetime
+import glob
 import os
 import shutil
 import string
@@ -103,14 +104,31 @@ class ConfigFileTemplate(string.Template):
     delimiter = "%"
 
 
+def backup_file(fname):
+    """Create a backup of a given file."""
+    for f in glob.glob("{}.old.*".format(fname)):
+        os.unlink(f)
+    bak_name = "{}.old.{}".format(
+        fname, datetime.datetime.now().isoformat())
+    shutil.copy(fname, bak_name)
+
+
+def copy_file(src, dest):
+    """Copy a file to a destination and make a backup before."""
+    if os.path.isdir(dest):
+        dest = os.path.join(dest, os.path.basename(src))
+    if os.path.isfile(dest):
+        backup_file(dest)
+    shutil.copy(src, dest)
+
+
 def copy_from_template(template, dest, context):
     """Create and copy a configuration file from a template."""
     now = datetime.datetime.now().isoformat()
     with open(template) as fp:
         buf = fp.read()
-    if os.path.exists(dest):
-        bak_name = "{}.{}.{}".format(dest, "old", now)
-        shutil.copy(dest, bak_name)
+    if os.path.isfile(dest):
+        backup_file(dest)
     with open(dest, "w") as fp:
         fp.write(
             "# This file was automatically installed on {}\n"