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

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

Windows favors multi-threading, which means that a service is implemented by one single process.

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.

Lack of documentation is becoming a problem for acceptance.

Adding functionality is not just a matter of adding code.

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