howto restart a service in postinst script (Stretch and newer)

[Harald Dunkel <harald.dunkel@aixigo.de>]

Hi folks,

the Debian Policy Manual still talks about "run levels" and
"init.d scripts" on 
https://www.debian.org/doc/debian-policy/ch-opersys.html#s-sysvinit .
No word about systemd and others.

What is the right way to restart a service from the postinst
script for Stretch and newer?

Reason for asking is: opensmtpd died once too often when it got
restarted via invoke-rc.d from a postinst script on my desktop 
PC.


Every helpful comment is highly appreciated
Harri