MIM to Entra migration and Active Directory writeback: What to consider
17.6.2025, 6 minutes read time
TL; DR: Writeback defines what the new identity model sends back to Active Directory during or after a migration from Microsoft Identity Manager (MIM) to Entra.
The scope should be based on application needs and kept as limited as possible.
Why Active Directory still matters
Active Directory still matters because many applications, integrations, and processes were built around it. Before authority is moved from MIM to Entra ID, the organization needs to understand which applications still depend on AD and which data they require.
The writeback decision should be tied to specific application needs. An application may require an AD group, a selected attribute, or a lifecycle state in AD. Anything beyond that increases dependency and should be avoided.
What the writeback decision controls
The writeback decision defines which identity outcomes are written to AD from the new model. This can include selected attributes, group membership, lifecycle state, or account status required by AD-dependent systems.
The decision should be made per application, population, group, attribute, or access scenario. The goal is to support required applications while keeping AD dependency as narrow as possible.
The risk of split authority
The main risk during a MIM to Entra migration is split authority.
In the target model, authority will move to Entra ID or to the identity governance layer above it. AD may still receive data, but it should have a clearly defined role. Legacy applications that still need to write to AD, should be rare, explicit, and controlled exceptions.
When more than one system can change the same identity outcome, the result can be overwritten changes, inconsistent group membership, reintroduced access, unclear audit trails, and difficult troubleshooting. Each identity outcome should therefore have a clear owner across MIM, Entra ID, AD, scripts, and manual processes.
How Identity Universe helps govern AD dependency
Identity Universe is a layer between HR and Entra ID that helps separate governance from target-system dependency.
Identity context, lifecycle state, policies, exceptions, and desired access can all be governed by Identity Universe and then be applied where it is needed, including in Entra ID for modern applications and in Active Directory for legacy dependencies.
This allows the organization to modernize identity logic while keeping AD writeback limited to specific needs. Only the users, groups, attributes, and lifecycle events required by a legacy application should be included.
For example, a Smart Collection may define the users who need access to a legacy AD-based application. The collections can drive the required AD group, while the same governance logic can also support modern Entra ID access.
What good looks like
A good AD and writeback strategy in a MIM to Entra migration has five characteristics.
First, dependencies are mapped in business terms, not only technical terms.
Second, authority is explicit. MIM, Entra ID, AD, scripts, and manual processes do not compete for the same outcome.
Third, the writeback is scoped and the team knows which populations, attributes, groups, and lifecycle events are included.
Fourth, writeback is tested and monitored during each wave of migration.
Fifth, dependency is reviewed over time, and transitional decisions do not become permanent by accident.
This is how organizations keep modernization practical while reducing risk.
FAQ
Should writeback be temporary?
Some writeback dependencies exist because an application, process, or integration has not yet been modernized. These dependencies should have an owner, a clear purpose, a defined scope, and a review point.
Without regular review, the MIM migration may be completed while old AD dependency patterns continue without a plan to reduce or remove them.
May writeback remain part of the operating model?
Some AD dependencies may remain for a long time where legacy systems are still business critical.
What does good look like?
A good AD writeback strategy in a MIM to Entra migration is clear and limited, and each dependency is tested, monitored, and reviewed over time. This keeps the migration practical while reducing long-term AD dependency.