Buying an email list is a terrible idea. It always was bad, but in these times when so much consent is required for marketing, I don’t understand how it can work. Just who are these people who’ve said to some third party: “Sure, you can sell my email address to unknown manufacturers”?
Who they are, of course, are people who’ve given their email address to a publisher, exhibition organiser or other presumably reputable organisation and not noticed that they’d also given permission for their contact details to be passed on. These aren’t a group of people whose inboxes you want to invade.
Third-party mailings that the recipients have signed up for, such as email newsletters and magazines, are a different matter. You can put your message in these and get some decent response. But please, make sure you’re measuring that response. Use Google’s Campaign Builder to create clickthrough URLs which can be identified and measured in Google Analytics. Set the campaign source to be something like “Widget World Newsletter”, the medium to be “email” and the “Campaign” to be “Widget World Newsletter August 2018”. Then you’ll be able to see the response instantly, under the Google Analytics “Acquisition > All Traffic > Source/Medium” report, perhaps with the “Secondary Dimension” set to “Campaign”.