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.
Qmail out of the box works fine, so people will want to use it regardless of licensing restrictions, even when the software does not ship with their system software.
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.
The challenge with Postfix, or with any piece of software, is to update software without introducing problems.
I want to avoid locking people into solutions that work only with Postfix. People should have a choice in what software they want to use with Postfix, be it anti-virus or otherwise.
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.
Adding functionality is not just a matter of adding code.
Lack of documentation is becoming a problem for acceptance.
Writing software that's safe even in the presence of bugs makes the challenge even more interesting.
Windows favors multi-threading, which means that a service is implemented by one single process.