When collecting email addresses, you need affirmative consent from prospects or customers. This practice is encouraged by the CAN-SPAM Act. To legally collect email addresses, you need to use landing pages and sign-up forms where you can ask visitors to click a box and give you permission to collect their email addresses. You can go one step further and inform them what you’ll do to keep their private data protected and how you’ll use their email addresses in the future. Purchasing email addresses from 3rd party companies, online directories, email address collection service providers is not an option if you want to keep things legal.