You may have noticed that a large number of email notifications from Moodle were delivered overnight, after (in some cases) a delay of many hours. The volume of email that Moodle is now generating required some tuning of our mail server configuration. It appears to be working much more smoothly now, so I am expecting that Moodle-related email will now be delivered in a more normal time-frame.
I will continue to monitor the system to see how it is doing.