The challenge
Six community health organisations were becoming one provider, each with its own Active Directory, its own Microsoft 365 tenant, its own naming conventions and its own record of who a person is.
That last part was the work. When six directories merge, some people already sit in two of them: a clinician working across two organisations, an administrator covering a second site. Thirteen people held accounts in more than one tenant. Five had the same account name in two different domains. Each is a question about a real person rather than a technical problem, and no mailbox could move until all eighteen were answered.
Underneath sat a question nobody could defer: build a new environment, or inherit one, against a merger timetable that was not going to wait.
The solution
The architecture decision was made once, in writing, and authorised. On 7 March 2024 the incoming chief executive approved building a new Active Directory environment in Azure and migrating every organisation into it, while retaining one organisation’s existing Microsoft 365 tenant and renaming it to the merged entity. The inherited tenant carried its own history and licensing, and it saved months. What matters is that the trade was chosen deliberately, by someone with the authority, on a date.
The next day the IT lead of the organisation whose tenant was being kept put a continuity risk on the record: consolidating into Azure meant abandoning a multi-cloud position and accepting single-vendor dependency.
Identity was resolved person by person before anything moved. The migration OU held 179 users: four disabled, thirteen whose primary domain lay elsewhere, and 162 migrated. Each of the five duplicate account names got a decision on which directory identity survives, and the obvious answer was not always the right one, because the surviving account determines what the person keeps. The thirteen holding accounts in more than one tenant had their content consolidated into a single new identity, which is a different exercise from moving a mailbox.
Every address changed at the same time as everything else. The merged organisation moved to a firstname.lastname convention on a new domain, so a person’s login, email address and display name all changed on the weekend their mailbox moved. Cutovers were staged by service area, with dates published to staff in advance.
The results
The two mailboxes that failed carried forwarding rules pointing at addresses that would not exist after the move; ignoring those rules let both complete, at the cost of those users’ rules. Shared mailboxes, resources and contacts were migrated as their own pass. The programme ran from November 2023 to May 2024, with Clouds Connected as technical lead under the managed services partner holding the client relationship.
The part worth carrying into the next merger is that the hard problem was never the mailboxes. It was eighteen people whose identities did not resolve cleanly, each needing a human decision.