High Quality Content by WIKIPEDIA articles! People tend to be much less bothered by spam slipping through filters into their mail box (false negatives), than having desired e-mail ("ham") blocked (false positives). Trying to balance false negatives (missed spams) vs false positives (rejecting good e-mail) is critical for a successful anti-spam system. As servers are not able to block all spam there are some tools for individual users to help control over this balance.