I've been cold emailing people for a few years now. Over that time, I've tried a bunch of tools, websites, and apps that claim to either scrub e-mails or give you verified e-mails of people.
Here are a few of my favorite ways to get people's emails, fast. This is obviously excluding extremely manual tactics like going to their personal website, GitHub, etc.
TL;DR: Use Google Sheets if you're guessing, and use RocketReach if you're not.