What are some alternatives?
Hunter - Find all the email addresses related to a domain
RocketReach - RocketReach allows you to lookup email and phone for 250+ million professionals.
Slik Prospector - Find anyone's email. No bounces.
FindThatLead - FINDTHATLEAD the ultimate tool for finding emails of people's profiles in linkedin . FindThatLead is the most straightforward way of finding leads of professionals from any sector to help you grow your business, career and professional .
Clearbit Connect - Clearbit Connect is a free extension that surfaces actionable information on the people who email you.
Leadfeeder Contacts - Find contact information for anonymous website visitors