Fix DJANGO_ALLOWED_HOSTS parsing

Closes #637.

postorius/mailman-web/settings.py

@@ -46,16 +46,14 @@ ADMINS = (
 SITE_ID = 1
 
 # Hosts/domain names that are valid for this site; required if DEBUG is False
-# See https://docs.djangoproject.com/en/1.8/ref/settings/#allowed-hosts
+# See https://docs.djangoproject.com/en/3.1/ref/settings/#allowed-hosts
 ALLOWED_HOSTS = [
     "localhost",  # Archiving API from Mailman, keep it.
-    # "lists.your-domain.org",
-    # Add here all production URLs you may have.
     "mailman-web",
     gethostbyname("mailman-web"),
     os.environ.get('SERVE_FROM_DOMAIN'),
-    os.environ.get('DJANGO_ALLOWED_HOSTS'),
 ]
+ALLOWED_HOSTS.extend(os.getenv("DJANGO_ALLOWED_HOSTS", "").split(","))
 
 # Mailman API credentials
 MAILMAN_REST_API_URL = os.environ.get('MAILMAN_REST_URL', 'http://mailman-core:8001')