diff --git a/bin/kolab_smtp_access_policy.py b/bin/kolab_smtp_access_policy.py
--- a/bin/kolab_smtp_access_policy.py
+++ b/bin/kolab_smtp_access_policy.py
@@ -17,6 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from six import string_types
 
 import datetime
 import os
@@ -266,7 +267,7 @@
 
             for search_attr in search_attrs:
                 if search_attr in rule_subject:
-                    if isinstance(rule_subject[search_attr], basestring):
+                    if isinstance(rule_subject[search_attr], string_types):
                         values.append(rule_subject[search_attr])
                     else:
                         values.extend(rule_subject[search_attr])
@@ -328,7 +329,7 @@
 
         rules = {'allow': [], 'deny': []}
 
-        if isinstance(policy, basestring):
+        if isinstance(policy, string_types):
             policy = [policy]
 
         for rule in policy:
@@ -513,7 +514,7 @@
                 return False
             else:
                 self.sasl_user = {'dn': sasl_users[0]}
-        elif isinstance(sasl_users, basestring):
+        elif isinstance(sasl_users, string_types):
             self.sasl_user = {'dn': sasl_users}
 
         if not self.sasl_user['dn']:
@@ -616,7 +617,7 @@
             else:
                 self.sender_user = {'dn': False}
 
-        elif isinstance(sender_users, basestring):
+        elif isinstance(sender_users, string_types):
             self.sender_user = {'dn': sender_users}
 
         if not self.sender_user['dn']:
@@ -711,7 +712,7 @@
                         return False
                     else:
                         self.sasl_user = {'dn': sasl_users[0]}
-                elif isinstance(sasl_users, basestring):
+                elif isinstance(sasl_users, string_types):
                     self.sasl_user = {'dn': sasl_users}
 
             # Possible values for the kolabDelegate attribute are:
@@ -892,7 +893,7 @@
 
                 return True
 
-        elif isinstance(recipients, basestring):
+        elif isinstance(recipients, string_types):
             _recipient = {'dn': recipients}
 
         # We have gotten an invalid recipient. We need to catch this case,
diff --git a/pykolab/cli/cmd_add_alias.py b/pykolab/cli/cmd_add_alias.py
--- a/pykolab/cli/cmd_add_alias.py
+++ b/pykolab/cli/cmd_add_alias.py
@@ -18,6 +18,7 @@
 #
 
 from __future__ import print_function
+from six import string_types
 
 import sys
 
@@ -110,7 +111,7 @@
     if secondary_rcpt_attr not in primary_recipient:
         auth.set_entry_attributes(primary_rcpt_domain, primary_recipient_dn, {secondary_rcpt_attr: [ secondary_rcpt_address ] })
     else:
-        if isinstance(primary_recipient[secondary_rcpt_attr], basestring):
+        if isinstance(primary_recipient[secondary_rcpt_attr], string_types):
             new_secondary_rcpt_attrs = [
                     primary_recipient[secondary_rcpt_attr],
                     secondary_rcpt_address
diff --git a/pykolab/cli/cmd_remove_mailaddress.py b/pykolab/cli/cmd_remove_mailaddress.py
--- a/pykolab/cli/cmd_remove_mailaddress.py
+++ b/pykolab/cli/cmd_remove_mailaddress.py
@@ -18,6 +18,7 @@
 #
 
 from __future__ import print_function
+from six import string_types
 
 import sys
 
@@ -67,7 +68,7 @@
 
     log.debug(_("Using the following mail attributes: %r") % (mail_attributes), level=8)
 
-    if isinstance(recipients, basestring):
+    if isinstance(recipients, string_types):
         recipient = recipients
 
         # Only a single recipient found, remove the address
diff --git a/pykolab/cli/commands.py b/pykolab/cli/commands.py
--- a/pykolab/cli/commands.py
+++ b/pykolab/cli/commands.py
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from six import string_types
 
 import os
 import sys
@@ -160,7 +161,7 @@
     else:
         command = cmd_name
 
-    if isinstance(aliases, basestring):
+    if isinstance(aliases, string_types):
         aliases = [aliases]
 
     if command in commands:
diff --git a/pykolab/cli/sieve/cmd_refresh.py b/pykolab/cli/sieve/cmd_refresh.py
--- a/pykolab/cli/sieve/cmd_refresh.py
+++ b/pykolab/cli/sieve/cmd_refresh.py
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from six import string_types
 
 import pykolab
 
@@ -215,7 +216,7 @@
     if not forward_active == False:
         forward_address_attr = conf.get('sieve', 'forward_address_attr')
         if forward_address_attr in user:
-            if isinstance(user[forward_address_attr], basestring):
+            if isinstance(user[forward_address_attr], string_types):
                 forward_addresses = [ user[forward_address_attr] ]
             elif isinstance(user[forward_address_attr], str):
                 forward_addresses = [ user[forward_address_attr] ]
diff --git a/pykolab/imap/__init__.py b/pykolab/imap/__init__.py
--- a/pykolab/imap/__init__.py
+++ b/pykolab/imap/__init__.py
@@ -16,7 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
-
+from six import string_types
 
 import logging
 import re
@@ -906,7 +906,7 @@
 
             return
 
-        if isinstance(acls, basestring):
+        if isinstance(acls, string_types):
             acls = [ acls ]
 
         old_acls = None
diff --git a/pykolab/plugins/sievemgmt/__init__.py b/pykolab/plugins/sievemgmt/__init__.py
--- a/pykolab/plugins/sievemgmt/__init__.py
+++ b/pykolab/plugins/sievemgmt/__init__.py
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from six import string_types
 
 import pykolab
 
@@ -227,7 +228,7 @@
         if not forward_active == False:
             forward_address_attr = conf.get('sieve', 'forward_address_attr')
             if forward_address_attr in user:
-                if isinstance(user[forward_address_attr], basestring):
+                if isinstance(user[forward_address_attr], string_types):
                     forward_addresses = [ user[forward_address_attr] ]
                 elif isinstance(user[forward_address_attr], str):
                     forward_addresses = [ user[forward_address_attr] ]
diff --git a/pykolab/setup/components.py b/pykolab/setup/components.py
--- a/pykolab/setup/components.py
+++ b/pykolab/setup/components.py
@@ -17,6 +17,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from six import string_types
 
 import os
 
@@ -224,7 +225,7 @@
     else:
         component = component_name
 
-    if isinstance(aliases, basestring):
+    if isinstance(aliases, string_types):
         aliases = [aliases]
 
     if component in components:
diff --git a/pykolab/xml/contact.py b/pykolab/xml/contact.py
--- a/pykolab/xml/contact.py
+++ b/pykolab/xml/contact.py
@@ -1,3 +1,5 @@
+from six import string_types
+
 import kolabformat
 import datetime
 import pytz
@@ -133,13 +135,13 @@
             return [x for x in self.emailAddresses()]
 
     def set_email(self, email, preferred_index=0):
-        if isinstance(email, basestring):
+        if isinstance(email, string_types):
             self.setEmailAddresses([email], preferred_index)
         else:
             self.setEmailAddresses(email, preferred_index)
 
     def add_email(self, email):
-        if isinstance(email, basestring):
+        if isinstance(email, string_types):
             self.add_emails([email])
         elif isinstance(email, list):
             self.add_emails(email)
diff --git a/pykolab/xml/event.py b/pykolab/xml/event.py
--- a/pykolab/xml/event.py
+++ b/pykolab/xml/event.py
@@ -1,3 +1,5 @@
+from six import string_types
+
 import datetime
 import icalendar
 import kolabformat
@@ -394,7 +396,7 @@
         return attendee.get_participant_status()
 
     def get_attendee(self, attendee):
-        if isinstance(attendee, basestring):
+        if isinstance(attendee, string_types):
             if attendee in [x.get_email() for x in self.get_attendees()]:
                 attendee = self.get_attendee_by_email(attendee)
 
@@ -892,7 +894,7 @@
             getattr(self, default_setter)(value)
 
     def set_ical_attendee(self, _attendee):
-        if isinstance(_attendee, basestring):
+        if isinstance(_attendee, string_types):
             _attendee = [_attendee]
 
         if isinstance(_attendee, list):
diff --git a/wallace/module_invitationpolicy.py b/wallace/module_invitationpolicy.py
--- a/wallace/module_invitationpolicy.py
+++ b/wallace/module_invitationpolicy.py
@@ -16,6 +16,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from six import string_types
 
 import datetime
 import os
@@ -712,7 +713,7 @@
 
     user_dn = auth.find_user_dn(email_address, True)
 
-    if isinstance(user_dn, basestring):
+    if isinstance(user_dn, string_types):
         log.debug(_("User DN: %r") % (user_dn), level=8)
     else:
         log.debug(_("No user record(s) found for %r") % (email_address), level=8)
diff --git a/wallace/modules.py b/wallace/modules.py
--- a/wallace/modules.py
+++ b/wallace/modules.py
@@ -18,6 +18,7 @@
 #
 
 from __future__ import print_function
+from six import string_types
 
 import os
 import sys
@@ -423,7 +424,7 @@
     else:
         module = name
 
-    if isinstance(aliases, basestring):
+    if isinstance(aliases, string_types):
         aliases = [aliases]
 
     if module in modules: