Using this plugin you can add emails to Gmail contacts, you can add emails from CSV or from user list or Manual enter emails. You need to create API key from Google console and insert in to plugin. You can select option easily using radio button.
PHP Requirements
Import emails to Gmail contacts plugin require 5.1.1 or higher
Deze plugin kan worden gedownload, zodat je hem op je zelf-gehoste WordPress-installatie kan gebruiken.