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.

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.

Defect-free software does not exist.

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

For many people my software is something that you install and forget. I like to keep it that way.

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