Sendmail used to run on something like 90% of the global Internet. And mail in the 1990s pretty much did work, pretty reliably. Would you have banked your site's security on the quality of Sendmail 8.6.12's code?
Slam dunk on that comment! Such systems, due to lots of debugging, can work reliably in a narrow set of use cases where specific features have massive use. Then there's the uncommon, usage scenarios and features that get much less debugging. Then there's all the patches they keep distributing to fix... "things."
And then the fact that safe, reliable code is only first step toward secure code where an intelligence, malicious person is targeting it. Totally different ballpark that neither Sendmail nor Cisco handled so well. Small shops like Sentinel and Secure64 did way better with a tiny fraction of the money. So, it has to be intentional for the extra profit at customers' expense.
