Nowadays, most Countries in the world have some anti-spam legislation. So, it's very important for e-mail marketers to comply with the anti-spam Laws of their country.
Furthermore, sending unsolicited e-mail could seriously compromise your business reputation.
In 2003, the United States drafted the CAN- SPAM Act (Controlling the Assault of Non-Solicited Pornography and Marketing).
In 2002, The European Union issued a "Privacy and Electronic Communications" directive, that requires businesses to gain prior consent before sending usolicited advertising e-mail to individuals. Anyway, each European Country has it's own national anti-spam legislation.
Detailed informations are available here: