The difference between personal where lost email isn't major against business where lost email could be lost income is the big point here.

I'd tend to agree, but the other way round. Lost income is no biggie, a company goes down and people move on. And an unanswered business email is usually chased-up anyway. But I've got several valued friendships that narrowed in the past to a single email or snail-mail before expanding again.

It's an interesting point to make. How much lost email are you willing to put up with to ensure that your spam fighting works?

Nil.

Peter