diff --git a/pykolab/auth/ldap/__init__.py b/pykolab/auth/ldap/__init__.py
--- a/pykolab/auth/ldap/__init__.py
+++ b/pykolab/auth/ldap/__init__.py
@@ -1859,10 +1859,8 @@
                         )
 
                 elif not entry_changes[result_attribute] == old_canon_attr:
-                    self.imap.user_mailbox_rename(
-                            old_canon_attr,
-                            entry_changes[result_attribute]
-                        )
+                    # do not rename an existing mailbox
+                    entry_changes[result_attribute] = old_canon_attr
 
         cache.get_entry(self.domain, entry)
 
@@ -2011,10 +2009,8 @@
                         )
 
                 else:
-                    self.imap.user_mailbox_rename(
-                            old_canon_attr,
-                            entry_changes[result_attribute]
-                        )
+                    # do not rename an existing mailbox
+                    entry_changes[result_attribute] = old_canon_attr
 
                 entry[result_attribute] = entry_changes[result_attribute]
                 cache.get_entry(self.domain, entry)
@@ -2026,10 +2022,8 @@
                         )
 
                 else:
-                    self.imap.user_mailbox_rename(
-                            old_canon_attr,
-                            entry[result_attribute]
-                        )
+                    # do not rename an existing mailbox
+                    entry[result_attribute] = old_canon_attr
 
                 cache.get_entry(self.domain, entry)
             else:
@@ -2199,10 +2193,8 @@
 
         if entry_changes.has_key(result_attribute) and not old_canon_attr == None:
             if not entry_changes[result_attribute] == old_canon_attr:
-                self.imap.user_mailbox_rename(
-                        old_canon_attr,
-                        entry_changes[result_attribute]
-                    )
+                # do not rename an existing mailbox
+                entry_changes[result_attribute] = old_canon_attr
 
         for key in entry_changes.keys():
             entry[key] = entry_changes[key]