Forum Discussion
Cross-tenant Migration
Yes, native cross-tenant mailbox migration is the supported method for this scenario, but EAC only manages the migration batches. The initial configuration still requires Exchange Online PowerShell to create the migration application, endpoint, organization relationships, scoped security group, and correctly attributed target MailUser objects; each migrating user also requires the Cross-Tenant User Data Migration add-on license.
Follow the Microsoft Learn procedure exactly and pilot one mailbox first. The main traps are mailboxes on hold, incorrect ExchangeGUID or X500/proxy addresses, permissions between users migrated in different batches, and the COMPANY-B domain cutover because a custom domain cannot be attached to both tenants simultaneously. Users must also recreate their Outlook profiles and resynchronize OST files after the move.
Treat SharePoint and Microsoft 365 Groups as separate projects because the mailbox process migrates only user-visible mailbox content and does not migrate Microsoft 365 Groups.