We have just discovered is that outgoing mail notifications did not work at all since the migration, except for users with a
@torproject.org address. It was a misconfiguration on our end that basically bounced all emails back to Discourse…
This has now been fixed, and email notifications should flow again, as much as other large providers like us to send email in the first place (e.g. right now Yahoo is unhappy with us). The notification backlog is huge: tens of thousands of emails. Discourse is retrying those as we speak, so those notifications accumulated in the past few weeks should slowly get out to everyone now.
This problem can be tracked in this GitLab issue:
As of 2023-07-20 15:00UTC, all pending mails have been sent and emails are going out normally.
Apologies for the trouble!