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Mainstream support for Dynamics 365 Customer Engagement on-premises ended. Extended support is a budget line, not a strategy. The migrations still in flight in 2026 are the hardest ones: heavily customized, regulatory, or air-gapped. Here is what works.

The Migration Tool is real and free

Microsoft’s Customer Engagement Migration Tool (also called the Dataverse migration tool) handles most metadata and data movement, including custom tables, plugins, workflows, and security roles. It is not the right answer for every migration but it is the right starting point. Treat what it cannot move as your true scope.

What it cannot move cleanly

  • Custom workflow activities compiled against the on-prem SDK. Recompile against the cloud SDK and re-register.
  • Plugin assemblies referencing on-prem SQL or IOrganizationService extensions that no longer exist.
  • IFD/ADFS authentication. Online uses Microsoft Entra exclusively.
  • Dialogs (deprecated since 2017 but still common in older systems). Rebuild as Power Apps or Power Automate.
  • Custom email router configurations. Replaced by server-side sync.

The data residency conversation

Online environments live in specific datacenter regions. Pick before you start. Moving data between regions post-migration is painful and may breach contracts. Verify with legal that the chosen region satisfies every jurisdiction’s requirements before signing.

The plugin sandbox shock

On-prem plugins can run in full-trust mode and read the file system, hit local SQL, and run arbitrary network calls. Online plugins run in sandbox mode with a 2-minute timeout, no file system, and outbound HTTP only to allowlisted endpoints (technically all endpoints but rate limited). Audit every plugin against the sandbox constraints before migration.

// On-prem (works): 
File.WriteAllText("C:\\logs\\out.txt", data);

// Online (fails silently or throws): 
// Replace with Application Insights logging
trace.Trace($"Data: {data}");

The reporting rebuild

SSRS reports running against on-prem direct-SQL fail in online. Rewrite as Power BI, Paginated Reports (which run on FetchXML), or model-driven views with charts. Plan for 30-50% of report inventory not surviving the move.

The cutover weekend

A typical large migration cutover: 12-hour data export, 6-hour transform, 8-hour import, 4-hour smoke test. Plan a 48-hour maintenance window with 24 hours of buffer. Communicate the read-only window to users in writing two weeks ahead.

What to do this week

Pull your on-prem plugin assembly list. For each, identify any reference to file system, direct SQL, or any class outside Microsoft.Xrm.Sdk. That is your refactor backlog. Start it now, not at cutover.

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