During my migration from GApps (prior to G Suite), I used this tool. I performed an initial migration before changing my MX records, then followed up a few days

During my migration from GApps (prior to G Suite), I used this tool. I performed an initial migration before changing my MX records, then followed up a few days later with a second (partial) migration to pick up a few slackers. I found the tool to be fast, comprehensive, and the partial migration was very effective.