Starting KumoMTA

Once KumoMTA has been installed and an initial policy script is in place, the server can be started with the following command:

sudo systemctl start kumomta

It can be enabled as a service with:

sudo systemctl enable kumomta

It can be started manually with:

 sudo /opt/kumomta/sbin/kumod --policy /opt/kumomta/etc/policy/init.lua --user kumod

Using sudo allows it to run as a privileged user so it can access port 25 which is needed to deliver via SMTP to the internet.
The daemon kumod is the MTA
The directive --policy makes kumod load the 'init.lua' file as configuration policy.
The --user directive allows the server to drop privileges after attaching to port 25 so that it does not continue to run as root.

For more detailed output, prepend KUMOD_LOG=kumod=info (or debug for more detail):

sudo KUMOD_LOG=kumod=info /opt/kumomta/sbin/kumod --policy /opt/kumomta/etc/policy/init.lua --user kumod

If all goes well, it should return a PID and drop you back to a Linux prompt.