diff --git a/core/admin/mailu/configuration.py b/core/admin/mailu/configuration.py
index c1444ee5..4d4ee3e9 100644
--- a/core/admin/mailu/configuration.py
+++ b/core/admin/mailu/configuration.py
@@ -153,7 +153,7 @@ class ConfigManager(dict):
         self.config['SESSION_COOKIE_HTTPONLY'] = True
         self.config['PERMANENT_SESSION_LIFETIME'] = timedelta(hours=int(self.config['SESSION_LIFETIME']))
         hostnames = [host.strip() for host in self.config['HOSTNAMES'].split(',')]
-        self.config['AUTH_RATELIMIT_EXEMPTION'] = set(ipaddress.ip_network(net.strip(), False) for net in self.config['AUTH_RATELIMIT_EXEMPTION'].split(','))
+        self.config['AUTH_RATELIMIT_EXEMPTION'] = set(ipaddress.ip_network(net.strip(), False) for net in self.config['AUTH_RATELIMIT_EXEMPTION'].split(',')) if self.config['AUTH_RATELIMIT_EXEMPTION'] else set()
         self.config['HOSTNAMES'] = ','.join(hostnames)
         self.config['HOSTNAME'] = hostnames[0]
         # update the app config itself