I have been watching the WireGuard project with interest for a couple of years. I like how WireGuard is constructed. A small code base that focus on the core functionality. The use of standard Linux networking tools and simple public/private keys.
Ansible role with commentary for setting up your own mail server with Postfix and Dovecot. This could be considered a part two of Mail relay, MX backup and spam filtering with Postfix. Many postfix configurations are identical between these setups.
If you run your own mail server it is a good idea to have a MX backup in place. When your mail server goes down or you need to upgrade it, the MX backup will step in and store all mail until the mail server is back up.
My article Running Drupal on Debian 8 with Apache 2.4, event MPM and PHP-FPM (via socks and proxy) is one of the most read on xdeb.org. Here is the updated version for Debian 9. I mention Drupal in the title but this setup should work well for most PHP based systems like Wordpress and Joomla etc.
Setting out to create a simple contact form turned out to involve more work than I anticipated. I need it for one of my new static sites. The examples I found was to old, lacking spam protection and/or relied on multiple/large libraries.
I prefer to store (archive) my mail locally. After moving my mail between mail clients a couple of time to many I decided to set up a local IMAP server. This will give me a mail client independent local storage that is in a standard format and future proof.