Zero-Loss Microsoft 365 Cross-Tenant Migration

Challenge

Sleep Clinics of America needed to migrate its entire Microsoft 365 environment — mailboxes, calendars, contacts, tasks, mailbox rules, OneDrive and SharePoint — into a different tenant (Arima Health), without downtime or data loss, while some user accounts were incompatible with standard cross-tenant migration tooling.

Architecture / Approach

Used Cross-Tenant Mailbox Migration (CTMM) for compatible users, and Microsoft Purview PST export/import for accounts blocked from CTMM. Migrated SharePoint content with SPMT and OneDrive with UDM. Coordinated a DNS cutover across MX, Autodiscover, SPF, DKIM and DMARC records to complete the transition cleanly.

My Role

Designed and led the end-to-end migration architecture and DNS cutover, working across mail, identity and file services.

Outcome

Completed the full mailbox, file and DNS migration across tenants with zero data loss, using a mixed-tooling approach to cover every account type in scope.

Technologies

• Microsoft 365
• Microsoft Purview
• SPMT
• UDM
• DNS (MX/SPF/DKIM/DMARC)