4 min read
A national care group operating through multiple subsidiaries, each with its own Microsoft 365 tenant, its own email domain, and its own way of doing things. Staff across Team Brain Injury Support, Team Medical, and Bespoke Health and Social Care were working on separate systems with no shared infrastructure, making collaboration between teams unnecessarily difficult.
Service: Managed IT Sector: Care
When the care group acquired and grew its subsidiaries over time, each organisation kept its own Microsoft 365 tenant. That meant separate email systems, separate user directories, and separate administration. Shared mailboxes for functions like timesheets, invoicing, and daily logs were scattered across tenants with no consistency.
For staff, this created practical problems. Sharing documents across subsidiaries meant emailing attachments back and forth. There was no shared calendar visibility, no unified address book, and no simple way to collaborate across teams. For IT, it meant managing multiple tenants, multiple licence agreements, and multiple sets of security policies with no central oversight.
The group also had former employees still appearing in directories and functional mailboxes that had evolved organically with no clear ownership. Nobody had taken the time to audit what existed across all three tenants, identify what was still needed, and bring it all together properly.
The migration needed to consolidate over 70 mailboxes into a single tenant without losing emails, contacts, calendars, or any of the data staff relied on daily. It also needed to happen with minimal disruption. A care organisation cannot afford to lose communication, even briefly.
We planned the migration in three phases, each with documented rollback procedures in case anything went wrong.
The first phase was preparation. We audited every mailbox across all three tenants, identified active users, flagged leavers, and mapped out shared mailboxes and distribution groups. We purchased Microsoft 365 Business Premium licences for all users on the target tenant and optimised DNS settings to reduce propagation time during the cutover.
The second phase was domain migration. Each subsidiary's email domain was moved to the consolidated tenant. This required careful DNS management to keep the mail flow interruption as short as possible. We scheduled the changes to minimise impact on frontline care staff who depend on email for shift coordination, safeguarding alerts, and family communication.
The third phase was the mailbox migration itself. We used CodeTwo Office 365 Migration to copy every mailbox one-to-one into the new tenant: emails, contacts, calendars, tasks, and notes. The tool's deduplication feature meant we could rescan and top up mailboxes without creating duplicates, which gave us flexibility to run the migration in stages rather than forcing a single big-bang cutover.
Alongside the mailbox migration, we standardised email signatures across the group and consolidated shared mailboxes into a single, logical structure. Functional mailboxes like timesheets, invoicing, and support were rationalised so every team knew exactly where to find what they needed.
Over 70 mailboxes were consolidated into a single Microsoft 365 tenant with no data loss and minimal disruption to care delivery. Staff across all three subsidiaries now share a unified address book, consistent security policies, and a single administrative platform.
The group went from managing three separate tenants with three sets of licences and three sets of policies to one coherent environment. IT administration is simpler, licence costs are more transparent, and security policies are applied consistently across every user.
For care staff on the ground, the change was straightforward. Their email still works, their contacts are still there, and their calendars carried over. The difference is that now they can collaborate across the wider group without workarounds.
70+ mailboxes migrated across three subsidiaries · Zero data loss · Three tenants consolidated into one · Standardised email signatures and shared mailboxes · Microsoft 365 Business Premium for all users
Related service: Managed IT