Learn how to whitelist your service's IP addresses in mailcow, in order to speed up SMTP sending.
Learn how to send emails from within a Docker container through the use of MSMTP.
A really interesting presentation from Dylan Beattie on how email has evolved over time. He covers pretty much everything from how email started, the first spam email, how most SMTP providers are not true to the actual specification, and even touching on SPF/DMARC protection etc.