Google will soon disable free access to legacy free domain mailboxes (G-Suite). When developing migration tool at inbox.eu it was major headache to implement migration from google. You either use web oauth2 login for each mailbox one by one (imagine pain moving thousands of mailboxes), or enable less secure apps option which now works unreliably or use not easy to obtain global service key to have full access to all domain (which admins do not want). Google makes really hard to move to another mailbox provider. I am actually updating migration tool to make it simpler to migrate