I manage two servers: one with the Grommunio Appliance running on Opensuse and a new server running on Debian 11.
Both with licenses and last updates.
Several users have informed me of recurring messages from Mailer-Daemon on both servers. Here is an example of this message:
This is the mail system at host myhost.com.I'm sorry to have to inform you that your message could notbe delivered to one or more recipients. It's attached below.For further assistance, please send mail to postmaster.If you do so, please include this problem report. You candelete your own text from the attached returned message. The mail system<invalid@invalid>: Host or domain name not found. Name service error for name=invalid type=AAAA: Host found but no data record of requested type
Digging a bit more the problem, it seems that this mail sent to invalid@invalid is triggered every time a message is sent to a Grommunio user with a reading confirmation.
Screenshot (in french where we can see a faulty "read confirmation" message with no email to.
I found a solution by hiding these messages in postfix but I guess I'm not the only one and that a more elegant solution must exist since the read confirmation doesn't seem to be transmitted to the original sender of the message.