Frameworks

Facebook Domain VerificationFacebook Domain Verification

Facebook Domain Verification Usage Statistics · Download List of All Websites using Facebook Domain Verification

Domain Verification provides a way for you to claim ownership of your domain in Facebook Business Manager.

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.