In terms of industry data, spam filters are generally seen as effective with about 99% effective, though Google has claimed they've achieved about 99.9% efficac

In terms of industry data, spam filters are generally seen as effective with about 99% effective, though Google has claimed they've achieved about 99.9% efficacy in the last few years, though there's some question as to how they are measuring that. The problem is, even at 99.9% efficacy, with around 50% of all e-mail being spam (that number used to be much higher, and there's some question as to whether the drop to 50% is a trend or a reflection of failures to detect/identify), that's still a lot of spam getting through.