diff --git a/modoboa/admin/api/v1/viewsets.py b/modoboa/admin/api/v1/viewsets.py
index 9fa0d4dd6..b1dc5aa84 100644
--- a/modoboa/admin/api/v1/viewsets.py
+++ b/modoboa/admin/api/v1/viewsets.py
@@ -192,6 +192,18 @@ class AccountViewSet(
         return Response(body)
 
 
+class AliasFilter(dj_filters.FilterSet):
+
+    domain = dj_filters.ModelChoiceFilter(
+        queryset=lambda request: models.Domain.objects.get_for_admin(request.user),
+        field_name="mailbox__domain",
+    )
+
+    class Meta:
+        model = models.Alias
+        fields = ["domain"]
+
+
 class AliasViewSet(
     GetThrottleViewsetMixin, lib_viewsets.RevisionModelMixin, viewsets.ModelViewSet
 ):
@@ -200,6 +212,10 @@ class AliasViewSet(
     Create a new alias instance.
     """
 
+    filter_backends = [
+        dj_filters.DjangoFilterBackend,
+    ]
+    filterset_class = AliasFilter
     permission_classes = [
         IsAuthenticated,
         DjangoModelPermissions,
@@ -209,14 +225,12 @@ class AliasViewSet(
     def get_queryset(self):
         """Filter queryset based on current user."""
         user = self.request.user
+        if user is None or user.is_anonymous:
+            return models.Alias.objects.none()
         ids = user.objectaccess_set.filter(
             content_type=ContentType.objects.get_for_model(models.Alias)
         ).values_list("object_id", flat=True)
-        queryset = models.Alias.objects.filter(pk__in=ids)
-        domain = self.request.query_params.get("domain")
-        if domain:
-            queryset = queryset.filter(domain__name=domain)
-        return queryset
+        return models.Alias.objects.filter(pk__in=ids, internal=False)
 
 
 class SenderAddressFilterSet(dj_filters.FilterSet):
diff --git a/modoboa/admin/api/v2/serializers.py b/modoboa/admin/api/v2/serializers.py
index 49dbb27ff..532093049 100644
--- a/modoboa/admin/api/v2/serializers.py
+++ b/modoboa/admin/api/v2/serializers.py
@@ -521,7 +521,8 @@ class WritableAccountSerializer(v1_serializers.WritableAccountSerializer):
         if not param_tools.get_global_parameter("enable_admin_limits", app="limits"):
             return
         del self.fields["domains"]
-        if self.context["request"].user.role in ["Resellers", "SuperAdmins"]:
+        user = self.context["request"].user
+        if not user.is_anonymous and user.role in ["Resellers", "SuperAdmins"]:
             self.fields["resources"] = WritableResourceSerializer(
                 many=True, required=False
             )
diff --git a/modoboa/admin/api/v2/viewsets.py b/modoboa/admin/api/v2/viewsets.py
index 16e7f2653..306f0bcb3 100644
--- a/modoboa/admin/api/v2/viewsets.py
+++ b/modoboa/admin/api/v2/viewsets.py
@@ -74,7 +74,9 @@ class DomainViewSet(
 
     def get_queryset(self):
         """Filter queryset based on current user."""
-        return models.Domain.objects.get_for_admin(self.request.user)
+        if self.request.user and not self.request.user.is_anonymous:
+            return models.Domain.objects.get_for_admin(self.request.user)
+        return models.Domain.objects.none()
 
     def get_serializer_class(self, *args, **kwargs):
         if self.action == "delete":
@@ -198,6 +200,8 @@ class AccountViewSet(v1_viewsets.AccountViewSet):
     def get_queryset(self):
         """Filter queryset based on current user."""
         user = self.request.user
+        if not user or user.is_anonymous:
+            return core_models.User.objects.none()
         ids = user.objectaccess_set.filter(
             content_type=ContentType.objects.get_for_model(user)
         ).values_list("object_id", flat=True)
@@ -271,14 +275,27 @@ class IdentityViewSet(GetThrottleViewsetMixin, viewsets.ViewSet):
         return response.Response({"status": status, "message": msg})
 
 
+class AliasFilter(dj_filters.FilterSet):
+
+    domain = dj_filters.ModelChoiceFilter(
+        queryset=lambda request: models.Domain.objects.get_for_admin(request.user),
+        field_name="domain__name",
+    )
+
+    class Meta:
+        model = models.Alias
+        fields = ["domain"]
+
+
 class AliasViewSet(v1_viewsets.AliasViewSet):
     """Viewset for Alias."""
 
-    filter_backends = (
+    filter_backends = [
+        dj_filters.DjangoFilterBackend,
         filters.OrderingFilter,
         filters.SearchFilter,
-        dj_filters.DjangoFilterBackend,
-    )
+    ]
+    filterset_class = AliasFilter
     pagination_class = pagination.CustomPageNumberPagination
     search_fields = ["address"]
     serializer_class = serializers.AliasSerializer
@@ -391,6 +408,8 @@ class AlarmViewSet(
     serializer_class = serializers.AlarmSerializer
 
     def get_queryset(self):
+        if self.request.user.is_anonymous:
+            return models.Alarm.objects.none()
         return (
             models.Alarm.objects.select_related("domain")
             .filter(domain__in=models.Domain.objects.get_for_admin(self.request.user))
diff --git a/modoboa/admin/handlers.py b/modoboa/admin/handlers.py
index 4634d0bce..35aa42561 100644
--- a/modoboa/admin/handlers.py
+++ b/modoboa/admin/handlers.py
@@ -236,11 +236,6 @@ def import_account_mailbox(sender, user, account, row, **kwargs):
             sender="import", context=domain, object_type="mailboxes"
         )
         account.save()
-        qset = models.Mailbox.objects.filter(address=mailbox, domain=domain)
-        if qset.exists():
-            raise exceptions.Conflict(
-                _("Mailbox {} already exists").format(account.email)
-            )
         if len(row) == 1:
             quota = None
         else:
@@ -274,16 +269,16 @@ def grant_access_to_all_objects(sender, account, role, **kwargs):
     """Grant all permissions if new role is SuperAdmin."""
     if role != "SuperAdmins":
         return
-    perm_models = [
-        core_models.User,
-        models.Domain,
-        models.DomainAlias,
-        models.Mailbox,
-        models.Alias,
+    querysets = [
+        core_models.User.objects.all(),
+        models.Domain.objects.all(),
+        models.DomainAlias.objects.all(),
+        models.Mailbox.objects.all(),
+        models.Alias.objects.filter(internal=False),
     ]
-    for model in perm_models:
+    for queryset in querysets:
         permissions.grant_access_to_objects(
-            account, model.objects.all(), ContentType.objects.get_for_model(model)
+            account, queryset, ContentType.objects.get_for_model(queryset.model)
         )
 
 
diff --git a/modoboa/admin/management/commands/subcommands/_repair.py b/modoboa/admin/management/commands/subcommands/_repair.py
index f17a54a50..3774e400a 100644
--- a/modoboa/admin/management/commands/subcommands/_repair.py
+++ b/modoboa/admin/management/commands/subcommands/_repair.py
@@ -56,7 +56,7 @@ def sometimes_objects_have_no_owner(**options):
         User.objects.all(),
         models.Domain.objects.all(),
         models.DomainAlias.objects.all(),
-        models.Alias.objects.filter(domain__isnull=False),
+        models.Alias.objects.filter(internal=False, domain__isnull=False),
         models.Mailbox.objects.filter(domain__isnull=False),
     )
     for qs in owned_models:
diff --git a/modoboa/admin/models/domain.py b/modoboa/admin/models/domain.py
index ad5bef7dd..24da5bba0 100644
--- a/modoboa/admin/models/domain.py
+++ b/modoboa/admin/models/domain.py
@@ -257,7 +257,7 @@ class Domain(mixins.MessageLimitMixin, AdminObject):
                 continue
             grant_access_to_object(account, mb)
             grant_access_to_object(account, mb.user)
-        for al in self.alias_set.all():
+        for al in self.alias_set.filter(internal=False):
             grant_access_to_object(account, al)
 
     def remove_admin(self, account):
diff --git a/modoboa/core/commands/templates/settings.py.tpl b/modoboa/core/commands/templates/settings.py.tpl
index 8d5ced9e5..ad9246b76 100644
--- a/modoboa/core/commands/templates/settings.py.tpl
+++ b/modoboa/core/commands/templates/settings.py.tpl
@@ -71,6 +71,7 @@ INSTALLED_APPS = (
     'corsheaders',
     'rest_framework',
     'rest_framework.authtoken',
+    'django_filters',
     'drf_spectacular',
     'phonenumber_field',
     'django_otp',
@@ -246,6 +247,9 @@ SPECTACULAR_SETTINGS = {
     'TITLE': 'Modoboa API',
     'VERSION': None,
     'SERVE_AUTHENTICATION': [],
+    'DEFAULT_FILTER_INSPECTORS': [
+        'drf_spectacular.contrib.django_filters.DjangoFilterBackendInspector',
+    ],
 }
 
 # Modoboa settings
diff --git a/test_project/test_project/settings.py b/test_project/test_project/settings.py
index e6871d18c..3a55d6b6a 100644
--- a/test_project/test_project/settings.py
+++ b/test_project/test_project/settings.py
@@ -79,6 +79,7 @@ INSTALLED_APPS = (
     "corsheaders",
     "rest_framework",
     "rest_framework.authtoken",
+    "django_filters",
     "drf_spectacular",
     "django_otp",
     "django_otp.plugins.otp_totp",
@@ -262,6 +263,9 @@ SPECTACULAR_SETTINGS = {
     "TITLE": "Modoboa API",
     "VERSION": None,
     "SERVE_AUTHENTICATION": [],
+    "DEFAULT_FILTER_INSPECTORS": [
+        "drf_spectacular.contrib.django_filters.DjangoFilterBackendInspector",
+    ],
 }
 
 # Modoboa settings