If we could update /etc/default/opendkim
to mention /lib/opendkim/opendkim.service.generate it would be at least something to save debugging hours. One can only wonder how many sysadmins are scratching their head right now, and how many will be after imminent upgrade to stretch. Best would be to run /lib/opendkim/opendkim.service.generate as needed, but that's a long shot. -Alexey