diff --git a/modoboa/admin/forms/domain.py b/modoboa/admin/forms/domain.py
index a1c649526..bad0668d7 100644
--- a/modoboa/admin/forms/domain.py
+++ b/modoboa/admin/forms/domain.py
@@ -239,22 +239,26 @@ class DomainFormOptions(forms.Form):
         da.role = "DomainAdmins"
         da.post_create(user)
 
+        dom_admin_username = self.cleaned_data["dom_admin_username"]
         mb = Mailbox(
-            address=self.cleaned_data["dom_admin_username"], domain=domain,
+            address=dom_admin_username, domain=domain,
             user=da, use_domain_quota=True
         )
         mb.set_quota(
             override_rules=user.has_perm("admin.change_domain"))
         mb.save(creator=user)
 
-        if domain.type == "domain" and self.cleaned_data["create_aliases"]:
+        condition = (
+            domain.type == "domain" and
+            self.cleaned_data["create_aliases"] and
+            dom_admin_username != "postmaster"
+        )
+        if condition:
             core_signals.can_create_object.send(
                 self.__class__, context=user, object_type="mailbox_aliases")
-            alias = Alias(
-                address=u"postmaster@{}".format(domain.name),
-                domain=domain, enabled=True
-            )
-            alias.save()
+            address = u"postmaster@{}".format(domain.name)
+            alias = Alias.objects.create(
+                address=address, domain=domain, enabled=True)
             alias.set_recipients([mb.full_address])
             alias.post_create(user)
 
diff --git a/modoboa/admin/tests/test_domain.py b/modoboa/admin/tests/test_domain.py
index bdf153d78..24906676d 100644
--- a/modoboa/admin/tests/test_domain.py
+++ b/modoboa/admin/tests/test_domain.py
@@ -55,10 +55,7 @@ class DomainTestCase(ModoTestCase):
             "dom_admin_username": "toto", "create_aliases": True,
             "type": "domain", "stepid": 'step3'
         }
-        self.ajax_post(
-            reverse("admin:domain_add"),
-            values
-        )
+        self.ajax_post(reverse("admin:domain_add"), values)
         dom = Domain.objects.get(name="pouet.com")
         da = User.objects.get(username="toto@pouet.com")
         self.assertIn(da, dom.admins)
@@ -69,6 +66,18 @@ class DomainTestCase(ModoTestCase):
         )
         self.assertTrue(da.can_access(al))
 
+        values = {
+            "name": "pouet2.com", "quota": 100, "create_dom_admin": "yes",
+            "dom_admin_username": "postmaster", "create_aliases": "yes",
+            "type": "domain", "stepid": "step3"
+        }
+        self.ajax_post(reverse("admin:domain_add"), values)
+        self.assertTrue(
+            User.objects.filter(username="postmaster@pouet2.com").exists())
+        self.assertFalse(
+            Alias.objects.filter(
+                address="postmaster@pouet2.com", internal=False).exists())
+
     def test_create_with_template_and_empty_quota(self):
         """Test the creation of a domain with a template and no quota"""
         values = {