diff --git a/core/admin/mailu/configuration.py b/core/admin/mailu/configuration.py
index d395073d..a997a8c7 100644
--- a/core/admin/mailu/configuration.py
+++ b/core/admin/mailu/configuration.py
@@ -156,6 +156,7 @@ class ConfigManager(dict):
         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(cidr, False) for cidr in (cidr.strip() for cidr in self.config['AUTH_RATELIMIT_EXEMPTION'].split(',')) if cidr)
+        self.config['MESSAGE_RATELIMIT_EXEMPTION'] = set([s for s in self.config['MESSAGE_RATELIMIT_EXEMPTION'].lower().replace(' ', '').split(',') if s])
         self.config['HOSTNAMES'] = ','.join(hostnames)
         self.config['HOSTNAME'] = hostnames[0]
         # update the app config itself
diff --git a/core/admin/mailu/internal/views/postfix.py b/core/admin/mailu/internal/views/postfix.py
index 2664f968..ed951943 100644
--- a/core/admin/mailu/internal/views/postfix.py
+++ b/core/admin/mailu/internal/views/postfix.py
@@ -149,7 +149,7 @@ def postfix_sender_login(sender):
 def postfix_sender_rate(sender):
     """ Rate limit outbound emails per sender login
     """
-    if sender in [s for s in flask.current_app.config.get('MESSAGE_RATELIMIT_EXEMPTION', '').lower().replace(' ', '').split(',') if s]:
+    if sender in flask.current_app.config['MESSAGE_RATELIMIT_EXEMPTION']:
         flask.abort(404)
     user = models.User.get(sender) or flask.abort(404)
     return flask.abort(404) if user.sender_limiter.hit() else flask.jsonify("450 4.2.1 You are sending too many emails too fast.")