Coming back to the topic of computer security, the TCP Wrapper is an example of such a safety net. I wrote it when my systems were under attack by someone who appeared to walk through walls.

Windows favors multi-threading, which means that a service is implemented by one single process.

The Postfix security model is based on keeping software simple and stupid.

The challenge with Postfix, or with any piece of software, is to update software without introducing problems.

In a previous life I wrote the software that controlled my physics experiments. That software had to deal with all kinds of possible failures in equipment. That is probably where I learned to rely on multiple safety nets inside and around my systems.

I don't expect an overnight change of all desktops to what the US Military used to call B3 level security. And even that would not stop users from shooting themselves into the foot.

Writing software that's safe even in the presence of bugs makes the challenge even more interesting.