Zot (Nomad) directory service
On the screenshot the delivery report of a direct message to firstname.lastname@example.org . One fact is that Nomad-Protocol apparently tries to deliver the message ONLY to the defunct channels on the hubs:
Background: I deleted the clone email@example.com exactly half a year ago. The information about the clone firstname.lastname@example.org I deleted here https://realtime.fyi/locs yesterday, because I see that the hub gerzilla.de does not exist anymore.
I note that I also did not get a notification about this reply  from Mario. I know I was expecting this notification, but didn't get one and I only discovered Mario's reply by accident. I suggest that you @mario post the delivery report for this message  here, while this delivery report is still available, so that people can research the cause of the missing notification.
After all, it could be that Nomad-Protocol in the example  is trying to deliver the notification to Zombi-clones that no longer exist, similar to the attached screenshot.