My biggest concern for my clients is the CAN-SPAM regulations – the laws that protect consumers from spam. For each and every violation of the CAN-SPAM Act of 2003, a business or person engaging in commercial emailing can be fined up to $11,000. (Source) Hosting and domain sellers that allow spam through their email systems can be fined as well as the original sender (according to one that I spoke with) so they cover themselves by deleting the offender. This happened to a psst client that basically lost his domain address because of people reporting spam from the domain.
Domains that send spam are also blacklisted so that no emails get through. I have seen this happen as well. It is very hard to get your domain approved again for sending email. It also hurts your business if NO emails get to their destinations.
Since the law is very unclear it is very important to protect your business by only sending list messages through email autoresponder companies.