Buying email lists is evil. Don't be evil.
Few things are as antithetical to good inbound marketing as purchasing a list of strangers' email addresses and blasting them with your latest campaign. You may get a short-term win, but emailing to a purchased list can be detrimental in the long run.
Beyond that, it's bad practice in general and causes frustration for the recipients, who haven't opted in to hear from you.
There are also two significant business risks associated with emailing to a purchased list:
1. It will damage your sender score
A company's sender score, which is tracked by Return Path, rates the reputation of every outgoing mail server IP address on a scale of 0-100. A company's sender score is determined by an algorithm that takes into account the ratio of undeliverable emails and spam reports for a company's sends.
Purchased lists are naturally higher in hard bounces and spam reports, and they can wreak havoc on your sender score. If your sender score drops, it severely limits your ability to have your future emails—even good, non-spammy ones—end up in recipients' inboxes.
That is what one bad email list can do to your sender score.