Just search customer company's domain name, for example 'homedepot.com', you'll get these results:
You have to register an account and log in to see the full email address. The free account is allowed to have maxium 150 requests. You can do a pre-search before logging in as a resistered user to see if they have the email addresses for your specific search. Then sign in to get the address. This will help you make efficient use of the free bonus.
A Chrome extension is offered by this service.