Merging Two Companies Into One Secure Microsoft 365 Tenant

A private equity-backed client needed to integrate an acquired company into its Microsoft 365 environment before a strict TSA deadline. The acquired business had its own M365 tenant, complex SharePoint structures, legacy Exchange configurations, and no standardised device management.

Cloudbliss began with a full discovery and planning phase, mapping tenant dependencies, shadow IT, licensing, SharePoint permissions, Teams structures, mail flow, and security policies. A detailed migration runbook was created to manage risk and give leadership visibility over the project timeline.

A coexistence model was then established so both organisations could continue collaborating during the transition. This included cross-tenant trust, mail flow coexistence, Global Address List synchronisation, and Teams guest access.

Cloudbliss then executed a pilot migration with a representative user group before moving into staged production waves. BitTitan MigrationWiz was used for mailbox migration, while ShareGate supported SharePoint and Teams content migration, including permission preservation and metadata handling.

The final phase focused on device and security transition. Devices were re-enrolled into Intune, Conditional Access policies were aligned, Defender for Endpoint was configured, and post-migration validation scripts were used to confirm data integrity before the source tenant was decommissioned.

Results

• 850 users migrated into a single Microsoft 365 tenant
• Migration completed two months ahead of the TSA deadline
• Estimated £300,000 in TSA extension fees avoided
• Zero data loss during mailbox migration
• Less than 15 minutes of user-facing downtime per wave
• £45,000 in annual licence savings identified
• Unified identity, security, collaboration, and device management environment created