Re:Improved Authentication for Email Encryption and Security
by Whitestrake on Monday December 05, 2016 @12:44AM
(#13103616)
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.
https://www.fastmail.com/help/receive/migratemail.html