Analytics and Tracking

Customer.ioCustomer.io

Customer.io Usage Statistics · Download List of All Websites using Customer.io

Email people automatically based on what they do (or don't do) in your app.

Marketing Automation

Email Hosting Providers

Google Apps for BusinessGoogle Apps for Business

Google Apps for Business Usage Statistics · Download List of All Websites using Google Apps for Business

Web-based email, calendar, and documents for teams. Renamed to Google Apps for Work, but now known as G Suite from Google Cloud.

Business Email Hosting

SPFSPF

SPF Usage Statistics · Download List of All Websites using SPF

The Sender Policy Framework is an open standard specifying a technical method to prevent sender address forgery.

Web Servers

ApacheApache

Apache Usage Statistics · Download List of All Websites using Apache

Apache has been the most popular web server on the Internet since April 1996.