settings: Add option to disable email deliverer.

zerver/management/commands/deliver_email.py

@@ -72,6 +72,12 @@ Usage: python manage.py deliver_email
     def handle(self, *args, **options):
         # TODO: this only acquires a lock on the system, not on the DB:
         # be careful not to run this on multiple systems.
+
+        # In the meantime, we have an option to prevent this job from
+        # running on >1 machine
+        if settings.EMAIL_DELIVERER_DISABLED:
+            return
+
         with lockfile("/tmp/zulip_email_deliver.lockfile"):
             while True:
                 # make sure to use utcnow, otherwise it gets confused when you set the time with utcnow(),

zproject/settings.py

@@ -144,6 +144,7 @@ DEFAULT_SETTINGS = {'TWITTER_CONSUMER_KEY': '',
                     'ENABLE_FEEDBACK': PRODUCTION,
                     'FEEDBACK_EMAIL': None,
                     'WELCOME_EMAIL_SENDER': None,
+                    'EMAIL_DELIVERER_DISABLED': False,
                     'ENABLE_GRAVATAR': True,
                     'DEFAULT_AVATAR_URI': '/static/images/default-avatar.png',
                     'AUTH_LDAP_SERVER_URI': "",