diff --git a/core/admin/mailu/internal/nginx.py b/core/admin/mailu/internal/nginx.py
index b7e246af..2ee6d9b3 100644
--- a/core/admin/mailu/internal/nginx.py
+++ b/core/admin/mailu/internal/nginx.py
@@ -94,11 +94,11 @@ def handle_authentication(headers):
         else:
             try:
                 user = models.User.query.get(user_email) if '@' in user_email else None
-                is_valid_user = user is not None
             except sqlalchemy.exc.StatementError as exc:
                 exc = str(exc).split('\n', 1)[0]
                 app.logger.warn(f'Invalid user {user_email!r}: {exc}')
             else:
+                is_valid_user = user is not None
                 ip = urllib.parse.unquote(headers["Client-Ip"])
                 if check_credentials(user, password, ip, protocol, headers["Auth-Port"]):
                     server, port = get_server(headers["Auth-Protocol"], True)
diff --git a/core/admin/mailu/internal/views/auth.py b/core/admin/mailu/internal/views/auth.py
index ab259864..426c0c49 100644
--- a/core/admin/mailu/internal/views/auth.py
+++ b/core/admin/mailu/internal/views/auth.py
@@ -32,7 +32,7 @@ def nginx_authentication():
     for key, value in headers.items():
         response.headers[key] = str(value)
     is_valid_user = False
-    if response.headers.get("Auth-User-Exists"):
+    if response.headers.get("Auth-User-Exists") == "True":
         username = response.headers["Auth-User"]
         if utils.limiter.should_rate_limit_user(username, client_ip):
             # FIXME could be done before handle_authentication()
diff --git a/towncrier/newsfragments/2284.bugfix b/towncrier/newsfragments/2284.bugfix
new file mode 100644
index 00000000..d264db89
--- /dev/null
+++ b/towncrier/newsfragments/2284.bugfix
@@ -0,0 +1 @@
+Fixed AUTH_RATELIMIT_IP not working on imap/pop3/smtp.
\ No newline at end of file