My reply is: the software has no known bugs, therefore it has not been updated.

Postfix keeps running even if one Postfix process dies; Windows requires that someone restarts the service.

Like all software, Qmail can survive only when it keeps up with changing requirements.

Lack of documentation is becoming a problem for acceptance.

Sure, but competition is good for the user.

When I write software, I know that it will fail, either due to my own mistake, or due to some other cause.

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