https://www.salehram.com/2017/03/14/a-story-of-a-project-3600-users-to-g-suite-in-60-days-day-5-going-full-speed-on-migration-users-change-from-domain-to-domain/
A story of a project: 3600 users to G Suite in 60 days! – Day 5: Going full speed on migration, Users change from domain to domain