https://romainl.github.io/the-patient-vimmer/0.html
https://romainl.github.io/the-patient-vimmer/1.html
https://romainl.github.io/the-patient-vimmer/2.html
https://romainl.github.io/the-patient-vimmer/3.html
https://romainl.github.io/the-patient-vimmer/4.html
https://romainl.github.io/the-patient-vimmer/5.html
https://romainl.github.io/the-patient-vimmer/6.html
https://romainl.github.io/the-patient-vimmer/7.html
https://romainl.github.io/the-patient-vimmer/8.html

Map functions are hard to "get" in the abstract. This looks at two mental models that helped me understand them better.

Switching from primitive types to product types can improve confidence in correctness and compiler errors, but not without a cost.

logrotate for docker logs

Good example for generating password using different wrappers or bindings of the crypt() function
I use this to manually change password in /etc/shadow for users created only as opensmtpd users which has no shell access (/usr/sbin/nologin)

The quickest way, using python3 is:
python -c 'import crypt; print(crypt.crypt("password",crypt.METHOD_SHA512))'

Concise example to setup an opensmtpd server with virtual domains and virtual users
Had some problems with the passwd table which where solved by following this example:
http://misc.opensmtpd.narkive.com/OpKS0DRj/table-passwd-invialid-without-the-shell

The guide is a bit too simplistic but covers some topics like spf and client configuration