diff --git a/tests/util/test_threepids.py b/tests/util/test_threepids.py
new file mode 100644

index 0000000000..5513724d87
--- /dev/null
+++ b/tests/util/test_threepids.py
@@ -0,0 +1,49 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Dirk Klimpel
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from synapse.util.threepids import canonicalise_email
+
+from tests.unittest import HomeserverTestCase
+
+
+class CanonicaliseEmailTests(HomeserverTestCase):
+    def test_no_at(self):
+        with self.assertRaises(ValueError):
+            canonicalise_email("address-without-at.bar")
+
+    def test_two_at(self):
+        with self.assertRaises(ValueError):
+            canonicalise_email("foo@foo@test.bar")
+
+    def test_bad_format(self):
+        with self.assertRaises(ValueError):
+            canonicalise_email("user@bad.example.net@good.example.com")
+
+    def test_valid_format(self):
+        self.assertEqual(canonicalise_email("foo@test.bar"), "foo@test.bar")
+
+    def test_domain_to_lower(self):
+        self.assertEqual(canonicalise_email("foo@TEST.BAR"), "foo@test.bar")
+
+    def test_domain_with_umlaut(self):
+        self.assertEqual(canonicalise_email("foo@Öumlaut.com"), "foo@öumlaut.com")
+
+    def test_address_casefold(self):
+        self.assertEqual(
+            canonicalise_email("Strauß@Example.com"), "strauss@example.com"
+        )
+
+    def test_address_trim(self):
+        self.assertEqual(canonicalise_email(" foo@test.bar "), "foo@test.bar")