In any sufficiently large dev team the technology choices trend toward zero. Because everyone has their "I will not work with this tech after dealing with its nasty bug."

Indeed. And products can get better and worse over time. If there's a consistent pattern of critical bugs at least with FOSS there is the possibility of forks and 3rd party patches.

Agreed! My personal bias against a system depends on if it failed at it's primary purpose or not. I've had a lot of things fail in a lot of ways and I'm generally pretty forgiving, but there are some things that are just inexcusable. Some examples:

* A popular (at the time) version control system started to silently overwrite files when it ran out of disk space. We discovered this when we retrieved source code that had parts of another file in it.

* A UPS vendor had a product that tested the battery by turning off the power. When the battery ultimately failed our servers were powered off automatically. This happened randomly about every 3 weeks (usually on a weekend evening). It took us months to find the cause.

I can't come back from these problems. So, if the system is a bit slow or crashes sometimes or has other weird problems, I'm OK with that. If it bites me specifically where it's supposed to protect me, it's out, forever.

I'm personally guilty of this mindset, but it's something I'm working on. After you get burned by a system, you know of the bug, and you can fix it. But the instinct is to switch to a new system, or to rewrite the system. That does get rid of all the bugs in the old system! But, in the process you've replaced them with brand new bugs that nobody has seen or heard from, until they decide to crawl into your mouth while you're asleep and you wake up in a panic. It's bugs all the way down, folks... this is software we're dealing with!

I think sendmail is the classic example of a program with so many bugs it had to be rewritten from scratch, and many people did. All of those alternatives, even qmail (widely debated: https://www.qualys.com/2020/05/19/cve-2005-1513/remote-code-...), ended up with a bug or security problem too. And they seem to have even fixed sendmail. It's still around and it doesn't take down the whole Internet every three weeks anymore. Wow! Sometimes there are just a million bugs, and you fix all one million of them, and then there aren't any more bugs.

In reality, the smart engineering choice is to know exactly what you are expecting from a specific system, and test it. Bugs, mistakes and even cosmic rays happen, so you must specifically test that it works. If you have a backup power system, test it.

sendmail is not a good example of a bad rewrite: 1st qmail is no more rewritten sendmail than Linux is rewrittnen Unix - qmail/exim/postfix just different software for the same use case. 2dn many other MTA (e. g. Postfix) managed to maintain much lower amount of security vulnerabilities than sendmail.

> It's still around and it doesn't take down the whole Internet every three weeks anymore.

Maybe that's because the vast majority of email no longer goes through sendmail.