Kirk almost always nails these posts and gets to them before me.
Buying a list and trying to get business that way is a long battle that's probably not worth it. He mentions open rates of 15% it's less than that if you buy a list AND it's pretty hard to even send them out, most providers will block you from "spamming people" Even with 15% open rates you'll do lucky to get a 1% click rate and less than that will "convert".
If you do use mail marketing again Kirk is right us it with your customer base, maybe offer a free service for referral to a new customer. Mailchimp or tiny letter is great. Or use Facebook and ask your current customers to "like" you.