diff --git a/docs/installation.rst b/docs/installation.rst
index 7c06bbb..f8e48e8 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -218,6 +218,9 @@ with the password ``my:password``, it would be represented as::
 
   smtp://someone%40example.com:my%3Apassword@smtp.example.com:25/
 
+The username and password can be omitted, with a URL in the form
+``smtp://host:port/``, if your mail server is a (properly firewalled!)
+unauthenticated relay.
 
 SendGrid
 ########
diff --git a/takahe/settings.py b/takahe/settings.py
index 3d7f0c4..28e512b 100644
--- a/takahe/settings.py
+++ b/takahe/settings.py
@@ -395,8 +395,10 @@ if SETUP.EMAIL_SERVER:
     elif parsed.scheme == "smtp":
         EMAIL_HOST = parsed.hostname
         EMAIL_PORT = parsed.port
-        EMAIL_HOST_USER = urllib.parse.unquote(parsed.username)
-        EMAIL_HOST_PASSWORD = urllib.parse.unquote(parsed.password)
+        if parsed.username is not None:
+            EMAIL_HOST_USER = urllib.parse.unquote(parsed.username)
+        if parsed.password is not None:
+            EMAIL_HOST_PASSWORD = urllib.parse.unquote(parsed.password)
         EMAIL_USE_TLS = as_bool(query.get("tls"))
         EMAIL_USE_SSL = as_bool(query.get("ssl"))
     else: