I hate to promote Google since they already rule the online world, but they do some things very well, e.g., their “unsubscribe” feature in Gmail. In a message, click on Show Details and you should see the option to “Unsubscribe from this sender.” The advantage of this is that it will be Gmail's servers talking to the spammer, not your PC, thereby removing the possibility of your being infected from merely visiting the spammer's “unsubscribe” page.