37. The machine-readable storage medium of claim 29 , further comprising instructions which, when executed by the one or more processors, cause the one or more processors to carry out the step of, when a particular list indicates an IP address range, setting a bit corresponding to the particular list in a particular list bit mask data structure corresponding to the IP address range.
37. The machine-readable storage medium of claim 29 , further comprising instructions which, when executed by the one or more processors, cause the one or more processors to carry out the step of, when a particular list indicates an IP address range, setting a bit corresponding to the particular list in a particular list bit mask data structure corresponding to the IP address range. 38. The machine-readable storage medium of claim 37 , wherein the step of setting the bit corresponding to the particular list is performed for each list of the two or more lists, and wherein sender corresponds to a particular IP address, the particular IP address is contained within a first IP address range that has associated with it a first list bit mask, the IP address is contained within a second IP address range associated with a second list bit mask, and wherein the machine-readable storage medium further comprises instructions which, when executed by the one or more processors, cause the one or more processors to carry out the step of determining which lists of the two or more lists indicate the message sender by performing the steps of: performing an or operation on the first list bit mask and second list bit mask to produce a third list bit mask; and determining what bits are set in the third list bit mask.