1. A method of detecting whether a first e-mail is undesirable, the method comprising: inputting the first e-mail to each of a plurality of constituent spam classifiers; obtaining at least one score from each of the plurality of constituent spam classifiers indicating the degree to which the first e-mail is deemed spam; obtaining a combined spam score from a combined spam classifier that takes as input the at least one score from the plurality of constituent spam classifiers, the combined spam classifier being computed automatically in accordance with a false-positive vs. false-negative tradeoff; and identifying the first e-mail as an undesirable e-mail if the combined spam score indicates that the first e-mail is undesirable.