1. A spam filtering method comprising employing at least one processor to perform the steps of: computing a relevance of a first anti-spam filter according to a relationship R=M−T×f(N,P), wherein M represents a training maturity of the first filter, T is an update age of the first filter indicative of a time period since a latest update of the first filter, wherein P is a false positive classification indicator of the first filter, N is a false negative classification indicator of the first filter, and wherein ƒ is a function of N and P; computing a relevance of a second anti-spam filter according to a training maturity of the second filter, an update age of the second filter indicative of a time period since the latest update of the second filter, a false positive classification indicator of the second filter, and a false negative classification indicator of the second filter; and determining whether an electronic communication is spam or non-spam according to a first result generated by applying the first anti-spam filter to the electronic communication, a second result generated by applying the second anti-spam filter to the electronic communication, the relevance of the first filter, and the relevance of the second filter.