We all hate e-mail spam, right? I even have the coolest software program that will help you combat spam and actually bounces the spam e-mail straight back to the user. (http://www.mailwasher.net)
However, one thing that we often fail to admit (except in private) is the importance of permission e-mail marketing, where the members of your mailing list have given you permission to contact them, or where they're past customers of yours. Obviously, these e-mail lists are always opt-out, so if someone chooses not to continue receiving information from you, they can easily get removed from the list.