There are laws against sending spam. There are even laws that you must adhere to when you send out email that was requested. No matter what type of email you are sending out, the chances are good that the anti-spam laws apply to you in some way.
In order to be in compliance with the anti-spam laws in various states in the US, each commercial email that you send must include your name or business name, your street address, city, state, zip code, and phone number. You must also include instructions that will allow the recipient to remove themselves from your mailing list. If you fail to do any of this, you are essentially breaking the law in various states – no matter what state or country you live in!
Protect yourself from spam complaints in any way that you can. Make sure that when a customer opts in to your mailing list that an email is sent requesting confirmation (double optin) before any other email is sent. Never use your autoresponder to send unsolicited commercial email!