He said himself that "a quick eye-ball sample says those failures mail are mostly spam that wasn’t classified right". Mostly? That means he already knows badly-encoded but legitimate email is not only possible but actually exists, so what's left to verify? Either you're okay with losing messages or you aren't.

I was responding to your use of the term 'hope', which made it sound like you thought this was just some blind stab in the dark. He has data, he's asking for more, and he's asking people to shoot him down if it's a dumb idea. It's hardly a faith-based effort.

And now you're parsing his sentence for subtle evidence that he secretly knows he's dropping some legitimate messages? Dude, he posted the fucking numbers himself. It's obvious that he's willing to drop some messages. He's asking how many he actually would be dropping and trying to work out if the benefits of "everything as UTF-8" outweighs the costs of dropping a message every now and then.

Either you're okay with losing messages or you aren't

Yeah, brilliant. There are already several reasons to drop messages (size, mangled headers, etc). He's pushing for another one.