We had some email delivery issues starting on 2017/12/10. Some time on that day emails started queueing due to delivery errors. We’ve resolved the issue and ended up deleting all queued up email earlier today. Email delivery from here on out should be good to go, but you may have missed email notifications / digest messages. Sorry for the inconvenience.
During the process of resolving the above issue, we also upgraded Discourse to the latest version.
Thanks & Happy Holidays!