In my experience, email verification gets you 99% of the way there. Strategically-placed honeypot form fields get you to 99.5%. I run a site that gets ~1.2 mi

In my experience, email verification gets you 99% of the way there. Strategically-placed honeypot form fields get you to 99.5%. I run a site that gets ~1.2 million visitors a month. YMMV.