Mailchimp Transactional Email (formerly Mandrill) is a reliable, scalable and secure delivery API for transactional emails from websites and applications.
Facebook Pixel helps organizations measure customer actions, build audiences and unlock optimisation tools. Facebook pixel is a snippet of JavaScript code that allows you to track visitor activity on your website.
Gmail is a free, advertising-supported email service offered as part of Google's G Suite, with 15GB of storage, color-coded inbox filters and unsend button.
Salesforce Heroku is part of the Salesforce Platform, enabling enterprises to store and leverage customer data in Salesforce for full-cycle CRM engagement.