1. A method for classifying email messages, the method comprising: providing multiple independent modules each of which is configured to analyze email messages; receiving an email message; using a plurality of the independent modules to determine a level of sameness of the received email message with one or more prior email messages, wherein each module being used determines a level of sameness in a different manner than the other modules being used, and wherein at least some of the modules being used are each assigned a non-zero weight indicative of the module's performance level; determining an overall level of sameness for the received email message by combining results of at least two of the plurality of independent modules using the non-zero weights assigned to the modules; evaluating the performance level for each of the independent modules that were used to determine the level of sameness for the received email message; comparing the performance levels evaluated for the independent modules that were used to determine the level of sameness for the received email message; adjusting the non-zero weights of at least two of the modules in response to comparing the performance levels, including increasing the non-zero weight of at least one of the modules and reducing the non-zero weight of at least another one of the modules; and using the overall level of sameness determined for the received email message to classify the received email message into a category.