1. A method for operation upon one or more data processors to assign a reputation to a messaging entity, comprising: receiving data that identifies one or more characteristics related to a messaging entity's communication; for each criterion in a set of criteria for use in discriminating between reputable and non-reputable classifications: determining, by one or more data processors, whether the criterion applies to the messaging entity; determining, by the one or more data processors, a first conditional probability that the messaging entity is a non-reputable messaging entity in response to determining that the criterion applies to the messaging entity; and determining, by the one or more data processors, a second conditional probability that the messaging entity is a reputable messaging entity in response to determining that the criterion applies to the messaging entity; determining, by the one or more data processors, a first probability that is indicative of the messaging entity being a non-reputable messaging entity, the first probably being determined from a product of the first conditional probabilities; determining, by the one or more data processors, a second probability that is indicative of the messaging entity being a reputable messaging entity, the second probably being determined from a product of the second conditional probabilities; determining, by the one or more data processors, a reputation score from the first and second probabilities, wherein the determined reputation score is indicative of reputation of the messaging entity; and wherein the determined reputation score is used in deciding what action is to be taken with respect to a communication associated with the messaging entity.