When installed on Ubuntu 20.04 LTS, Virtualmin configures Postfix to use
milter_protocol = 2
which works for OpenDKIM.
But I also added Rspamd to block spam during incoming smtp, and that requires manually editing
/etc/postfix/main.cf to set
milter_protocol = 6.
Ordinarily this would be a harmless manual tweak.
However, any time DKIM is re-initialized, Virtualmin silently changes
milter_protocol back to 2, and Rspamd breaks.
So here’s a suggested fix: Initialize
milter_protocol to any desired level when Virtualmin is initially installed, but don’t change it subsequently. The idea is to not override a manual tweak.