Probably not illegal, since it's a private for of communication. There are very few laws that govern the internet except for Kiddie porn stuff. Most lawmakers are unsure of what direction to go in regulating the internet and ISP's, and have very little technical skill or knowlage themselves. When they do research, they ask big companies like Microsquish for information and policy suggestions, not the common person. Most often spam filters are set to the number of addresses listed on a simgle email. Most companies let you decide the number, or put them in a special folder for review (MSN uses "Bulk Mail"). If your ISP is taking your choice away, it's probably time to change prviders. If they take this choice away, they may be taking away others you don't know about (like automatically bouncing email from specific sites they find "offensive").