Finally, Ruby has more than one implementation. Finding a hole in one implementation says nothing about the language overall.
(That's the only vulnerability ever found in qmail, and it wasn't exploitable --- Postfix has had much worse).
The point is that writing simple software in C is possible. But writing complex software is very very hard.
If you took a class with Bernstein, you might be familiar with the ISP whose entire mail operation, including customer POP and virtual hosting, I ran on qmail --- that'd be EnterAct. So yeah, I'm not buying your "qmail is too simple to matter" argument. If you want to chase it down, I'll be happy to show you where the last few Sendmail vulnerabilities were found. Clue: not in the crazy Sendmail features that qmail lacks.
But that's besides the point. You didn't answer my question.
Name a piece of code of comparable complexity to qmail that's never had an integer overflow. Here's another hint: Perl isn't one of them.
It has.