However, writing software without defects is not sufficient. In my experience, it is at least as difficult to write software that is safe - that is, software that behaves reasonably under adverse conditions.
Writing software that's safe even in the presence of bugs makes the challenge even more interesting.
One bug in an SMTP server can open up the whole machine for intrusion.
The challenge with Postfix, or with any piece of software, is to update software without introducing problems.
When I write software, I know that it will fail, either due to my own mistake, or due to some other cause.
For many people my software is something that you install and forget. I like to keep it that way.
Postfix keeps running even if one Postfix process dies; Windows requires that someone restarts the service.
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.
I was going to visit IBM for six months as a visiting scientist. Now, six months is a lot of time, so I came with a whole list of projects that I might want to work on.
Adding functionality is not just a matter of adding code.