Buying an email list is a chancy way to reach new potential clients since you do not know whether you have acquired a quality list and therefore may get a low return on investment.
If you do decide to buy a mailing list, large companies that sell email lists are usually better at providing a trustworthy opt-in email list but you will be paying premium prices for it. See the previous article, http://www.blindmonkeymedia.com/marketing-articles/89-email-marketing-basics-the-dangers, for more details about the dangers of purchasing an email list.
The best way to build an email marketing list is to build it yourself thru your website(s) using one or several of these methods:
Offer to send visitors your newsletter. The best way to do that is to have an email capture box on your website where visitors can opt-in to receive a specific type of email about a product or service.
The second is the way is to have an interactive website where visitors can interact with you or one another. To do that, a visitor must wither sign up or submit some basic information like name and email address. If you have that can of website, then you got yourself a mailing list.
Whenever someone interacts on your site, make sure that this person understands that by deciding to either post or take part in the forum or leave a comment that his email can be used to receive information or promotional emails from your website.
The third way to build a mailing list is by holding a contest or some kind of sweepstake. The prize does not have to be large or expensive. Just use your imagination. The catch in this free contest or sweepstake is that by entering they agree to receive advertising emails from you.
Another way to acquire an email list to use a software that can scan the internet for email addresses. Keep in mind that this method falls in the gray area in terms spamming. In theory, the software is supposed to be able to pick up emails according to your target keywords. What such a software does is look for emails that are on a page that matches your keywords and captures that email address.
The problem with this method is that most of the email addresses acquired will not be a person’s personal email but rather business emails.
It is good if you are a business-to-business company but bad if you are a business-to-consumer company.