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

At the time the Sendmail program had a very poor reputation with respect to security, with four root vulnerabilities per year for two successive years.

Most of the effort in the software business goes into the maintenance of code that already exists.

One bug in an SMTP server can open up the whole machine for intrusion.

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.

Sure, but competition is good for the user.

This will surprise some of your readers, but my primary interest is not with computer security. I am primarily interested in writing software that works as intended.