We recently completed a migration from Ubuntu 14.04 to 16.04.
Apparently, 16.04 does not include/support the 'dkim-filter' described in your documentation:
OpenDKIM is installed, running and listening on port 8891:
root@www3:~# netstat -tapn |grep 8891
tcp 0 0 127.0.0.1:8891 0.0.0.0:* LISTEN 11854/opendkim
However, attempting to configure DKIM using:
Virtualmin → E-Mail Settings → DomainKeys Identified Mail
Failed to save DKIM settings : Systemd service opendkim cannot be created unless a command is given
So I have disabled it for now.
Do you have any clues for me?
I would also like to get DMARC working...
Thanks in advance,