diff --git a/doc/integration/imap_and_smtp.rst b/doc/integration/imap_and_smtp.rst
index cbeee2c60..06f84b8fe 100644
--- a/doc/integration/imap_and_smtp.rst
+++ b/doc/integration/imap_and_smtp.rst
@@ -330,69 +330,16 @@ Trigger
 
 As indicated on `Dovecot's wiki
 <http://wiki2.dovecot.org/Quota/Dict>`_, you need a trigger to
-properly update the quota. Unfortunately, the provided example won't
-work for Modoboa. You should use the following one instead:
+properly update the quota.
 
-.. sourcecode:: sql
+A working copy of this trigger is available on `Modoboa's website
+<http://modoboa.org/resources/modoboa_postgres_trigger.sql>`_.
 
-  CREATE OR REPLACE FUNCTION merge_quota() RETURNS TRIGGER AS $$
-  BEGIN
-    IF NEW.messages < 0 OR NEW.messages IS NULL THEN
-      -- ugly kludge: we came here from this function, really do try to insert
-      IF NEW.messages IS NULL THEN
-        NEW.messages = 0;
-      ELSE
-        NEW.messages = -NEW.messages;
-      END IF;
-      return NEW;
-    END IF;
-
-    LOOP
-      UPDATE admin_quota SET bytes = bytes + NEW.bytes,
-        messages = messages + NEW.messages
-        WHERE username = NEW.username;
-      IF found THEN
-        RETURN NULL;
-      END IF;
-
-      BEGIN
-        IF NEW.messages = 0 THEN
-          RETURN NEW;
-        ELSE
-          NEW.messages = - NEW.messages;
-          return NEW;
-        END IF;
-      EXCEPTION WHEN unique_violation THEN
-        -- someone just inserted the record, update it
-      END;
-    END LOOP;
-  END;
-  $$ LANGUAGE plpgsql;
-
-  CREATE OR REPLACE FUNCTION set_mboxid() RETURNS TRIGGER AS $$
-  DECLARE
-    mboxid INTEGER;
-  BEGIN
-    SELECT admin_mailbox.id INTO STRICT mboxid FROM admin_mailbox INNER JOIN core_user ON admin_mailbox.user_id=core_user.id WHERE core_user.username=NEW.username;
-    UPDATE admin_quota SET mbox_id = mboxid
-      WHERE username = NEW.username;
-    RETURN NULL;
-  END;
-  $$ LANGUAGE plpgsql;
-
-  DROP TRIGGER IF EXISTS mergequota ON admin_quota;
-  CREATE TRIGGER mergequota BEFORE INSERT ON admin_quota
-     FOR EACH ROW EXECUTE PROCEDURE merge_quota();
-
-  DROP TRIGGER IF EXISTS setmboxid ON admin_quota;
-  CREATE TRIGGER setmboxid AFTER INSERT ON admin_quota
-     FOR EACH ROW EXECUTE PROCEDURE set_mboxid();
-
-Copy this example into a file (for example: :file:`quota-trigger.sql`) on
-server running postgres and execute the following commands::
+Download this file and copy it on the server running postgres. Then,
+execute the following commands::
 
   $ su - postgres
-  $ psql [modoboa database] < /path/to/quota-trigger.sql
+  $ psql [modoboa database] < /path/to/modoboa_postgres_trigger.sql
   $ exit
   
 Replace ``[modoboa database]`` by the appropriate value.
diff --git a/modoboa/extensions/admin/migrations/0038_auto__add_field_mailbox_quota_value__del_field_quota_mbox.py b/modoboa/extensions/admin/migrations/0038_auto__add_field_mailbox_quota_value__del_field_quota_mbox.py
new file mode 100644
index 000000000..aacb7383a
--- /dev/null
+++ b/modoboa/extensions/admin/migrations/0038_auto__add_field_mailbox_quota_value__del_field_quota_mbox.py
@@ -0,0 +1,135 @@
+# -*- coding: utf-8 -*-
+from south.utils import datetime_utils as datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+        # Adding field 'Mailbox.quota_value'
+        db.add_column(u'admin_mailbox', 'quota_value',
+                      self.gf('django.db.models.fields.related.ForeignKey')(to=orm['admin.Quota'], null=True),
+                      keep_default=False)
+
+        # Deleting field 'Quota.mbox'
+        db.delete_column(u'admin_quota', 'mbox_id')
+
+
+    def backwards(self, orm):
+        # Deleting field 'Mailbox.quota_value'
+        db.delete_column(u'admin_mailbox', 'quota_value_id')
+
+        # Adding field 'Quota.mbox'
+        db.add_column(u'admin_quota', 'mbox',
+                      self.gf('django.db.models.fields.related.OneToOneField')(related_name='quota_value', unique=True, null=True, to=orm['admin.Mailbox']),
+                      keep_default=False)
+
+
+    models = {
+        'admin.alias': {
+            'Meta': {'ordering': "['domain__name', 'address']", 'unique_together': "(('address', 'domain'),)", 'object_name': 'Alias'},
+            'address': ('django.db.models.fields.CharField', [], {'max_length': '254'}),
+            'aliases': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['admin.Alias']", 'symmetrical': 'False'}),
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'domain': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'extmboxes': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mboxes': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['admin.Mailbox']", 'symmetrical': 'False'})
+        },
+        'admin.domain': {
+            'Meta': {'ordering': "['name']", 'object_name': 'Domain'},
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100'}),
+            'quota': ('django.db.models.fields.IntegerField', [], {})
+        },
+        'admin.domainalias': {
+            'Meta': {'object_name': 'DomainAlias'},
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100'}),
+            'target': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"})
+        },
+        'admin.mailbox': {
+            'Meta': {'object_name': 'Mailbox'},
+            'address': ('django.db.models.fields.CharField', [], {'max_length': '252'}),
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'domain': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'quota': ('django.db.models.fields.PositiveIntegerField', [], {}),
+            'quota_value': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Quota']", 'null': 'True'}),
+            'use_domain_quota': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['core.User']"})
+        },
+        'admin.mailboxoperation': {
+            'Meta': {'object_name': 'MailboxOperation'},
+            'argument': ('django.db.models.fields.TextField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mailbox': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Mailbox']", 'null': 'True', 'blank': 'True'}),
+            'type': ('django.db.models.fields.CharField', [], {'max_length': '20'})
+        },
+        'admin.objectdates': {
+            'Meta': {'object_name': 'ObjectDates'},
+            'creation': ('django.db.models.fields.DateTimeField', [], {'auto_now_add': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'last_modification': ('django.db.models.fields.DateTimeField', [], {'auto_now': 'True', 'blank': 'True'})
+        },
+        'admin.quota': {
+            'Meta': {'object_name': 'Quota'},
+            'bytes': ('django.db.models.fields.BigIntegerField', [], {'default': '0'}),
+            'messages': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'username': ('django.db.models.fields.EmailField', [], {'max_length': '254', 'primary_key': 'True'})
+        },
+        u'auth.group': {
+            'Meta': {'object_name': 'Group'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '80'}),
+            'permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'})
+        },
+        u'auth.permission': {
+            'Meta': {'ordering': "(u'content_type__app_label', u'content_type__model', u'codename')", 'unique_together': "((u'content_type', u'codename'),)", 'object_name': 'Permission'},
+            'codename': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '50'})
+        },
+        u'contenttypes.contenttype': {
+            'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},
+            'app_label': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '100'})
+        },
+        u'core.objectaccess': {
+            'Meta': {'unique_together': "(('user', 'content_type', 'object_id'),)", 'object_name': 'ObjectAccess'},
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_owner': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'object_id': ('django.db.models.fields.PositiveIntegerField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['core.User']"})
+        },
+        u'core.user': {
+            'Meta': {'ordering': "['username']", 'object_name': 'User'},
+            'date_joined': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'email': ('django.db.models.fields.EmailField', [], {'max_length': '254', 'blank': 'True'}),
+            'first_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'groups': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Group']", 'symmetrical': 'False', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_active': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_local': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_staff': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'is_superuser': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'last_login': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'last_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'password': ('django.db.models.fields.CharField', [], {'max_length': '256'}),
+            'user_permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '254'})
+        }
+    }
+
+    complete_apps = ['admin']
\ No newline at end of file
diff --git a/modoboa/extensions/admin/migrations/0039_set_mailbox_quota_value.py b/modoboa/extensions/admin/migrations/0039_set_mailbox_quota_value.py
new file mode 100644
index 000000000..bd42e28ee
--- /dev/null
+++ b/modoboa/extensions/admin/migrations/0039_set_mailbox_quota_value.py
@@ -0,0 +1,130 @@
+# -*- coding: utf-8 -*-
+from south.utils import datetime_utils as datetime
+from south.db import db
+from south.v2 import DataMigration
+from django.db import models
+
+class Migration(DataMigration):
+
+    def forwards(self, orm):
+        "Write your forwards methods here."
+        for mailbox in orm.Mailbox.objects.all():
+            quota, created = orm.Quota.objects.get_or_create(
+                pk="%s@%s" % (mailbox.address, mailbox.domain.name)
+            )
+            mailbox.quota_value = quota
+            mailbox.save()
+
+    def backwards(self, orm):
+        "Write your backwards methods here."
+        for mailbox in orm.Mailbox.objects.all():
+            mailbox.quota_value = None
+            mailbox.save()
+
+    models = {
+        'admin.alias': {
+            'Meta': {'ordering': "['domain__name', 'address']", 'unique_together': "(('address', 'domain'),)", 'object_name': 'Alias'},
+            'address': ('django.db.models.fields.CharField', [], {'max_length': '254'}),
+            'aliases': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['admin.Alias']", 'symmetrical': 'False'}),
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'domain': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'extmboxes': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mboxes': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['admin.Mailbox']", 'symmetrical': 'False'})
+        },
+        'admin.domain': {
+            'Meta': {'ordering': "['name']", 'object_name': 'Domain'},
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100'}),
+            'quota': ('django.db.models.fields.IntegerField', [], {})
+        },
+        'admin.domainalias': {
+            'Meta': {'object_name': 'DomainAlias'},
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100'}),
+            'target': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"})
+        },
+        'admin.mailbox': {
+            'Meta': {'object_name': 'Mailbox'},
+            'address': ('django.db.models.fields.CharField', [], {'max_length': '252'}),
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'domain': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'quota': ('django.db.models.fields.PositiveIntegerField', [], {}),
+            'quota_value': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Quota']", 'null': 'True'}),
+            'use_domain_quota': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['core.User']"})
+        },
+        'admin.mailboxoperation': {
+            'Meta': {'object_name': 'MailboxOperation'},
+            'argument': ('django.db.models.fields.TextField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mailbox': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Mailbox']", 'null': 'True', 'blank': 'True'}),
+            'type': ('django.db.models.fields.CharField', [], {'max_length': '20'})
+        },
+        'admin.objectdates': {
+            'Meta': {'object_name': 'ObjectDates'},
+            'creation': ('django.db.models.fields.DateTimeField', [], {'auto_now_add': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'last_modification': ('django.db.models.fields.DateTimeField', [], {'auto_now': 'True', 'blank': 'True'})
+        },
+        'admin.quota': {
+            'Meta': {'object_name': 'Quota'},
+            'bytes': ('django.db.models.fields.BigIntegerField', [], {'default': '0'}),
+            'messages': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'username': ('django.db.models.fields.EmailField', [], {'max_length': '254', 'primary_key': 'True'})
+        },
+        u'auth.group': {
+            'Meta': {'object_name': 'Group'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '80'}),
+            'permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'})
+        },
+        u'auth.permission': {
+            'Meta': {'ordering': "(u'content_type__app_label', u'content_type__model', u'codename')", 'unique_together': "((u'content_type', u'codename'),)", 'object_name': 'Permission'},
+            'codename': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '50'})
+        },
+        u'contenttypes.contenttype': {
+            'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},
+            'app_label': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '100'})
+        },
+        u'core.objectaccess': {
+            'Meta': {'unique_together': "(('user', 'content_type', 'object_id'),)", 'object_name': 'ObjectAccess'},
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_owner': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'object_id': ('django.db.models.fields.PositiveIntegerField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['core.User']"})
+        },
+        u'core.user': {
+            'Meta': {'ordering': "['username']", 'object_name': 'User'},
+            'date_joined': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'email': ('django.db.models.fields.EmailField', [], {'max_length': '254', 'blank': 'True'}),
+            'first_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'groups': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Group']", 'symmetrical': 'False', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_active': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_local': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_staff': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'is_superuser': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'last_login': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'last_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'password': ('django.db.models.fields.CharField', [], {'max_length': '256'}),
+            'user_permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '254'})
+        }
+    }
+
+    complete_apps = ['admin']
+    symmetrical = True
diff --git a/modoboa/extensions/admin/migrations/0040_auto__chg_field_mailbox_quota_value.py b/modoboa/extensions/admin/migrations/0040_auto__chg_field_mailbox_quota_value.py
new file mode 100644
index 000000000..7aebef23d
--- /dev/null
+++ b/modoboa/extensions/admin/migrations/0040_auto__chg_field_mailbox_quota_value.py
@@ -0,0 +1,125 @@
+# -*- coding: utf-8 -*-
+from south.utils import datetime_utils as datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+
+        # Changing field 'Mailbox.quota_value'
+        db.alter_column(u'admin_mailbox', 'quota_value_id', self.gf('django.db.models.fields.related.ForeignKey')(default=0, to=orm['admin.Quota']))
+
+    def backwards(self, orm):
+
+        # Changing field 'Mailbox.quota_value'
+        db.alter_column(u'admin_mailbox', 'quota_value_id', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['admin.Quota'], null=True))
+
+    models = {
+        'admin.alias': {
+            'Meta': {'ordering': "['domain__name', 'address']", 'unique_together': "(('address', 'domain'),)", 'object_name': 'Alias'},
+            'address': ('django.db.models.fields.CharField', [], {'max_length': '254'}),
+            'aliases': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['admin.Alias']", 'symmetrical': 'False'}),
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'domain': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'extmboxes': ('django.db.models.fields.TextField', [], {'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mboxes': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['admin.Mailbox']", 'symmetrical': 'False'})
+        },
+        'admin.domain': {
+            'Meta': {'ordering': "['name']", 'object_name': 'Domain'},
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100'}),
+            'quota': ('django.db.models.fields.IntegerField', [], {})
+        },
+        'admin.domainalias': {
+            'Meta': {'object_name': 'DomainAlias'},
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '100'}),
+            'target': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"})
+        },
+        'admin.mailbox': {
+            'Meta': {'object_name': 'Mailbox'},
+            'address': ('django.db.models.fields.CharField', [], {'max_length': '252'}),
+            'dates': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.ObjectDates']"}),
+            'domain': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Domain']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'quota': ('django.db.models.fields.PositiveIntegerField', [], {}),
+            'quota_value': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Quota']"}),
+            'use_domain_quota': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['core.User']"})
+        },
+        'admin.mailboxoperation': {
+            'Meta': {'object_name': 'MailboxOperation'},
+            'argument': ('django.db.models.fields.TextField', [], {}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'mailbox': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['admin.Mailbox']", 'null': 'True', 'blank': 'True'}),
+            'type': ('django.db.models.fields.CharField', [], {'max_length': '20'})
+        },
+        'admin.objectdates': {
+            'Meta': {'object_name': 'ObjectDates'},
+            'creation': ('django.db.models.fields.DateTimeField', [], {'auto_now_add': 'True', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'last_modification': ('django.db.models.fields.DateTimeField', [], {'auto_now': 'True', 'blank': 'True'})
+        },
+        'admin.quota': {
+            'Meta': {'object_name': 'Quota'},
+            'bytes': ('django.db.models.fields.BigIntegerField', [], {'default': '0'}),
+            'messages': ('django.db.models.fields.IntegerField', [], {'default': '0'}),
+            'username': ('django.db.models.fields.EmailField', [], {'max_length': '254', 'primary_key': 'True'})
+        },
+        u'auth.group': {
+            'Meta': {'object_name': 'Group'},
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '80'}),
+            'permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'})
+        },
+        u'auth.permission': {
+            'Meta': {'ordering': "(u'content_type__app_label', u'content_type__model', u'codename')", 'unique_together': "((u'content_type', u'codename'),)", 'object_name': 'Permission'},
+            'codename': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '50'})
+        },
+        u'contenttypes.contenttype': {
+            'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},
+            'app_label': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '100'})
+        },
+        u'core.objectaccess': {
+            'Meta': {'unique_together': "(('user', 'content_type', 'object_id'),)", 'object_name': 'ObjectAccess'},
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['contenttypes.ContentType']"}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_owner': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'object_id': ('django.db.models.fields.PositiveIntegerField', [], {}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'to': u"orm['core.User']"})
+        },
+        u'core.user': {
+            'Meta': {'ordering': "['username']", 'object_name': 'User'},
+            'date_joined': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'email': ('django.db.models.fields.EmailField', [], {'max_length': '254', 'blank': 'True'}),
+            'first_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'groups': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Group']", 'symmetrical': 'False', 'blank': 'True'}),
+            u'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_active': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_local': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_staff': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'is_superuser': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'last_login': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'last_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'password': ('django.db.models.fields.CharField', [], {'max_length': '256'}),
+            'user_permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': u"orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '254'})
+        }
+    }
+
+    complete_apps = ['admin']
\ No newline at end of file
diff --git a/modoboa/extensions/admin/models/mailbox.py b/modoboa/extensions/admin/models/mailbox.py
index 82abbc13a..233fde8e1 100644
--- a/modoboa/extensions/admin/models/mailbox.py
+++ b/modoboa/extensions/admin/models/mailbox.py
@@ -16,6 +16,17 @@ from .base import AdminObject
 from .domain import Domain
 
 
+class Quota(models.Model):
+    """Mailbox current quota usage.
+    """
+    username = models.EmailField(primary_key=True, max_length=254)
+    bytes = models.BigIntegerField(default=0)
+    messages = models.IntegerField(default=0)
+
+    class Meta:
+        app_label = 'admin'
+
+
 class MailboxManager(Manager):
 
     def get_for_admin(self, admin, squery=None):
@@ -43,7 +54,7 @@ class MailboxManager(Manager):
             qf = Q(pk__in=ids) & qf
         else:
             qf = Q(pk__in=ids)
-        return self.get_query_set().filter(qf)
+        return self.get_query_set().select_related().filter(qf)
 
 
 class Mailbox(AdminObject):
@@ -53,6 +64,7 @@ class Mailbox(AdminObject):
     )
     quota = models.PositiveIntegerField()
     use_domain_quota = models.BooleanField(default=False)
+    quota_value = models.ForeignKey(Quota, to_field="username")
     domain = models.ForeignKey(Domain)
     user = models.ForeignKey(User)
 
@@ -95,7 +107,7 @@ class Mailbox(AdminObject):
 
         We ask dovecot to give us this information because there are
         several patterns to understand and we don't want to implement
-        them.        
+        them.
         """
         hm = parameters.get_admin("HANDLE_MAILBOXES", raise_error=False)
         if hm is None or hm == "no":
@@ -179,11 +191,10 @@ class Mailbox(AdminObject):
 
     def get_quota(self):
         """Get quota limit.
-        
+
         :rtype: int
         """
-        q = Quota.objects.get(username=self.full_address)
-        return int(q.bytes / 1048576)
+        return int(self.quota_value.bytes / 1048576)
 
     def get_quota_in_percent(self):
         """Get current quota usage.
@@ -192,8 +203,9 @@ class Mailbox(AdminObject):
         """
         if not self.quota:
             return 0
-        q = Quota.objects.get(username=self.full_address)
-        return int(q.bytes / float(self.quota * 1048576) * 100)
+        return int(
+            self.quota_value.bytes / float(self.quota * 1048576) * 100
+        )
 
     def post_create(self, creator):
         from modoboa.lib.permissions import grant_access_to_object
@@ -209,11 +221,16 @@ class Mailbox(AdminObject):
                 grant_access_to_object(admin, self.user)
 
     def save(self, *args, **kwargs):
-        super(Mailbox, self).save(*args, **kwargs)
+        """Custom save.
+
+        We just make sure a quota record is defined for this mailbox.
+        """
         try:
             q = self.quota_value
         except Quota.DoesNotExist:
-            Quota.objects.create(mbox=self, username=self.full_address)
+            self.quota_value, created = Quota.objects.get_or_create(
+                username=self.full_address)
+        super(Mailbox, self).save(*args, **kwargs)
 
     def delete(self, keepdir=False):
         """Custom delete method
@@ -257,17 +274,6 @@ def mailbox_deleted_handler(sender, **kwargs):
             alias.delete()
 
 
-class Quota(models.Model):
-    username = models.EmailField(primary_key=True, max_length=254)
-    bytes = models.BigIntegerField(default=0)
-    messages = models.IntegerField(default=0)
-
-    mbox = models.OneToOneField(Mailbox, related_name="quota_value", null=True)
-
-    class Meta:
-        app_label = 'admin'
-
-
 class MailboxOperation(models.Model):
     mailbox = models.ForeignKey(Mailbox, blank=True, null=True)
     type = models.CharField(