ZeroBounce.net does it's best to append additional data to your emails like "First Name, Last Name, Gender, Etc". The more information you know about your customer, the better you can communicate with them.
We gather this information through reliable third-party sources we have contracts with. Unfortunately, we will not be able to provide this information for all e-mail addresses, because we don't have it and are unable to retrieve it. It's a nice feature we provide for free and sometimes we achieve over 80% data appends rate and other times under 10% depending on the list uploaded.