Defect-free software does not exist.
One bug in an SMTP server can open up the whole machine for intrusion.
Like all software, Qmail can survive only when it keeps up with changing requirements.
Adding functionality is not just a matter of adding code.
The challenge with Postfix, or with any piece of software, is to update software without introducing problems.
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.