I started looking in to use of OpenSMPTD for a mail server and have
installed it from Debian packages.
In the process of reading a blog article by the current developer I
discovered the upstream is now at version 6.6.2p1+ after some serious
security issues were discovered by SSL Labs (Qualys). Note that Debian
10 is only at version 6.0.3p1! See the source at:
https://github.com/OpenSMTPD/OpenSMTPD
I would like to install from source but I wonder if that is such a
smart move, especially when we now use systemd and the source is set
up with the traditional GNU automake system and I don't see any
provision for systemd. I don't grok systemd very well and usually
rely on others for the proper setup.
I have asked for help on the OpenSMTPD mailing list, but I suggested
my first effort would be to use the systemd setup used by the Debian
installation (with appropriate renaming). I haven't received an answer
yet.