diff --git a/modoboa/admin/api.py b/modoboa/admin/api.py
index d36184980..bfe452cf7 100644
--- a/modoboa/admin/api.py
+++ b/modoboa/admin/api.py
@@ -3,7 +3,10 @@
 from django.contrib.contenttypes.models import ContentType
 
 from rest_framework import viewsets
+from rest_framework.decorators import list_route
+from rest_framework.exceptions import ParseError
 from rest_framework.permissions import DjangoModelPermissions
+from rest_framework.response import Response
 
 from modoboa.core import models as core_models
 
@@ -35,7 +38,7 @@ class AccountViewSet(viewsets.ModelViewSet):
         """Return a serializer."""
         if self.request.method == "GET":
             return serializers.AccountSerializer
-        return serializers.CreateAccountSerializer
+        return serializers.WritableAccountSerializer
 
     def get_queryset(self):
         """Filter queryset based on current user."""
@@ -48,3 +51,16 @@ class AccountViewSet(viewsets.ModelViewSet):
     def perform_destroy(self, instance):
         """Add custom args to delete call."""
         instance.delete(self.request.user)
+
+    @list_route()
+    def exists(self, request):
+        """Check if account exists."""
+        email = request.GET.get("email")
+        if not email:
+            raise ParseError("email not provided")
+        if not core_models.User.objects.filter(email=email).exists():
+            data = {"exists": False}
+        else:
+            data = {"exists": True}
+        serializer = serializers.AccountExistsSerializer(data)
+        return Response(serializer.data)
diff --git a/modoboa/admin/serializers.py b/modoboa/admin/serializers.py
index 730fe9d31..473395656 100644
--- a/modoboa/admin/serializers.py
+++ b/modoboa/admin/serializers.py
@@ -65,7 +65,13 @@ class AccountSerializer(serializers.ModelSerializer):
         return account.group
 
 
-class CreateAccountSerializer(AccountSerializer):
+class AccountExistsSerializer(serializers.Serializer):
+    """Simple serializer used with existence checks."""
+
+    exists = serializers.BooleanField()
+
+
+class WritableAccountSerializer(AccountSerializer):
     """Serializer to create account."""
 
     class Meta(AccountSerializer.Meta):
@@ -74,7 +80,7 @@ class CreateAccountSerializer(AccountSerializer):
 
     def __init__(self, *args, **kwargs):
         """Adapt fields to current user."""
-        super(CreateAccountSerializer, self).__init__(*args, **kwargs)
+        super(WritableAccountSerializer, self).__init__(*args, **kwargs)
         user = self.context["request"].user
         self.fields["role"] = serializers.ChoiceField(
             choices=permissions.get_account_roles(user))
diff --git a/modoboa/admin/tests/api.py b/modoboa/admin/tests/api.py
index a060d96a6..7c610f774 100644
--- a/modoboa/admin/tests/api.py
+++ b/modoboa/admin/tests/api.py
@@ -256,3 +256,19 @@ class AccountAPITestCase(ModoAPITestCase):
         self.assertFalse(
             core_models.User.objects.filter(pk=account.pk).exists())
         self.assertFalse(domadmin.can_access(account))
+
+    def test_account_exists(self):
+        """Validate /exists/ service."""
+        url = reverse("external_api:account-exists")
+        response = self.client.get(
+            "{}?email={}".format(url, "user@test.com"))
+        self.assertEqual(response.status_code, 200)
+        content = json.loads(response.content)
+        self.assertTrue(content["exists"])
+        response = self.client.get(
+            "{}?email={}".format(url, "pipo@test.com"))
+        self.assertEqual(response.status_code, 200)
+        content = json.loads(response.content)
+        self.assertFalse(content["exists"])
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 400)