1. A method for analyzing email messages, comprising: (a) for each of a plurality of received email messages, using a plurality of modules to each independently determine a module output indicative of a level of sameness of the received email message with one or more prior email messages, and determining an overall level of sameness of the received email message with one or more prior email messages by combining the module outputs of at least two of the plurality of modules using non-zero weights assigned to the modules in dependence on performance levels of the modules; (b) classifying each of the plurality of received email messages into one of a plurality of different categories by (b.1) determining, based on the overall level of sameness determined for the received email message, whether the received email message is considered to be the same as one of the one or more prior email messages that has already been classified into one of the categories; (b.2) if the received email message is not considered to be the same as one of the one or more prior email messages that has already been classified into one of the categories, then performing a set of computations to thereby classify the received email message into one of the categories; and (b.3) if the received email message is considered to be the same as one of the one or more prior email messages that has already been classified into one of the categories, then classifying the received email message into the same category as the prior email message that the received email message is considered to be the same as, without performing the set of computations for the received email message; wherein steps (a) and/or (b) are performed using at least one processor.