What are some alternatives?
Hunter - Find all the email addresses related to a domain
CleanEmail - CleanEmail is an online service that empowers you to take control of your mailbox.
Slik Prospector - Find anyone's email. No bounces.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Clearbit Connect - Clearbit Connect is a free extension that surfaces actionable information on the people who email you.
MailClark - The Slack bot for external communications