Informational email marketing is quite different from promotional email marketing and they have very different goals. If your goals are to build your reputation and relationships, then buying email addresses is definitely not for you!
Reputable bulk ESPs (email service providers) insist that you have permission to email the contacts you add to your databases with them. So if you buy mailing lists, there's the potential risk of having your bulk email account shut down. The trigger for this would be a high number of bounces on your first send.
Aside from being a nuisance, there are other downsides as well. You don't even know if you're buying valid email addresses! Daley Progress has 17 imaginary employees who regularly receive email because someone made up their names.