Am confused by some of these flag notifications I see on many automated e-mails, including some self-hosted discourse forum sites but not discourse server hosted ones.
Believe these may have something to do with the way servers are configured, may not necessarily be a bug or problem but from my side this does look like one:
Not posting the whole technical sender address here, these are typically just a lot of random numbers and letters.
I don’t think that’s a Discourse bug. The error message will occur when email is not properly configured. If you are in contact with the admins of any sites you are seeing this on, let them know about the problem. To fix it, they should make sure that all steps in the Setting Up Email section if the install guide have been completed: https://github.com/discourse/discourse/blob/main/docs/INSTALL-cloud.md#2-setting-up-email. My guess is that they haven’t added valid SPF and DKIM records to their domain.
You could also try pointing them to this topic: Email delivery configuration checklist.
Thanks I have reported these to some administrators.