Email lists are useful for communicating with groups, but it is difficult to refine the intended audience. When planning a surprise party, for example, it is time consuming to delete the guest of honor's address from the multiple e-mail lists one wants to contact. We have built a tool that makes it easy to modify e-mail lists and, thus, contact specific audiences. The tool provides the computational mechanism for solving 'e-mail equations'. An equation for the aforementioned example could be ((partyPeople@mit.edu & dancers@mit.edu) - joe@mit.edu). This equation would resolve to address all recipients of two e-mail lists except for joe@mit.edu. E-mail list addition, subtraction, intersection and xor can be computed with our tool.