If you buy a list from outside and blast email out to those email addresses you are SPAMMING. There i something you should know about SPAM.
In the United States, most states enacted anti-spam laws during the late 1990s and early 2000s. Many of these have since been pre-empted by the less restrictive CAN-SPAM Act of 2003 ("CAN-SPAM").
Spam is legally permissible according to CAN-SPAM, provided it meets certain criteria: a "truthful" subject line, no forged information in the technical headers or sender address, and other minor requirements. If the spam fails to comply with any of these requirements it is illegal. Aggravated or accelerated penalties apply if the spammer harvested the email addresses using methods described earlier.
A review of the effectiveness of CAN-SPAM in 2005 by the Federal Trade Commission (the agency charged with CAN-SPAM enforcement) stated that the amount of sexually explicit spam had significantly decreased since 2003 and the total volume had begun to level off. Senator Conrad Burns, a principal sponsor, noted that "Enforcement is key regarding the CAN-SPAM legislation." In 2004, less than one percent of spam complied with CAN-SPAM. In contrast to the FTC evaluation, many observers view CAN-SPAM as having failed in its purpose of reducing spam.[