OpenSMTPd package is already available, but not the latest version 6.4.1 .

However since 6.4.0 the configuration file syntax has been completely reworked, breaking compatibility with previous configuration files
and OpenSMTPD now depends on LibreSSL as an SSL library (efforts will no longer be done to support OpenSSL too).

Do you plan to provide OpenSMTPd, maybe in a new package “opensmtpd-6.4”, with the new features (including the incoming ECDSA support) ?

https://www.opensmtpd.org/announces/release-6.4.1.txt
https://www.opensmtpd.org/announces/release-6.4.0.txt

(from redmine: issue id 10605, created on 2019-06-23)