diff --git a/tests/rest/client/test_register.py b/tests/rest/client/test_register.py
index 859051cdda7..46911cb1a0c 100644
--- a/tests/rest/client/test_register.py
+++ b/tests/rest/client/test_register.py
@@ -22,6 +22,7 @@
 import datetime
 import os
 from typing import Any, Dict, List, Tuple
+from unittest.mock import AsyncMock
 
 import pkg_resources
 
@@ -35,6 +36,7 @@
 )
 from synapse.api.errors import Codes
 from synapse.appservice import ApplicationService
+from synapse.http.server import HttpServer
 from synapse.rest.client import account, account_validity, login, logout, register, sync
 from synapse.server import HomeServer
 from synapse.storage._base import db_to_json
@@ -45,11 +47,20 @@
 from tests.unittest import override_config
 
 
+# Let's override the email register servlet to mock send_email, since the smtp server doesn't really exists
+def override_email_register_servlet(hs: "HomeServer", http_server: HttpServer) -> None:
+    if hs.config.worker.worker_app is None and hs.config.email.can_verify_email:
+        email_register_servlet = register.EmailRegisterRequestTokenRestServlet(hs)
+        email_register_servlet.already_in_use_mailer.send_email = AsyncMock()  # type: ignore[method-assign]
+        email_register_servlet.register(http_server)
+
+
 class RegisterRestServletTestCase(unittest.HomeserverTestCase):
     servlets = [
         login.register_servlets,
         register.register_servlets,
         synapse.rest.admin.register_servlets,
+        override_email_register_servlet,
     ]
     url = b"/_matrix/client/r0/register"