Migrations Pro
How it works

From read-only assessment to signed reconciliation

Five phases. You can stop after the assessment — it costs nothing and writes nothing.

  1. 01

    Assessment

    Read-only discovery against both tenants. Nothing is written, so it's safe to run before any commercial commitment.

    • Mailbox, archive, OneDrive, SharePoint, Groups and Teams inventory
    • Sizes and item counts per object, with a throughput projection
    • Risk findings — oversized items, unmapped identities, missing targets
  2. 02

    Mapping and scope

    Decide what moves and where it lands. Source objects are matched to destination identities before anything copies.

    • Automatic matching by UPN, with manual override where identities differ
    • Optional auto-provisioning of destination users that don't exist yet
    • Batches you control — pilot a handful before committing the estate
  3. 03

    Migration

    Bulk copy runs under Exchange's migration throttle budgets. Passes resume rather than restart, so an interruption costs a scan, not a re-copy.

    • Idempotent by design — re-running skips what's already in the destination
    • Large items routed through a chunked upload path automatically
    • Throttling is honoured, not fought: pauses are expected, not failures
  4. 04

    Coexistence and delta sync

    Scheduled passes copy what has arrived since the last successful run, so the destination stays current while you plan cutover.

    • Runs on a schedule you set — six hours by default
    • Only fetches new mail, so it stays fast as the estate grows
    • A full re-sync recovers anything historical that delta wouldn't revisit
  5. 05

    Verification and cutover

    Completeness is established by comparing messages, not counts, and recorded in a signed report.

    • Message-ID set difference across primary, archive and recoverable items
    • Explicit list of anything present at source and absent at destination
    • Domain cutover orchestration with a documented rollback path
Before you start

Four things that decide how this goes

These are destination-tenant settings. None of them are optional for a large migration, and all of them are cheaper to do first than to diagnose afterwards.

Suspend destination retention

Retention policies act on migrated mail as soon as it lands — migrated mail keeps its original dates, so a two-year rule applies to most of it immediately. Put mailboxes on retention hold first.

Raise the maximum message size

Set it to the Exchange Online maximum of 150 MB. Allow around six hours for the change to propagate before migrating.

Request a throttling exemption

On both tenants. Throttling is the single biggest factor in how long a migration takes — far more than platform capacity.

Grant admin consent on both tenants

Consent given under the wrong account fails silently. Use a private window signed in as the Global Administrator of the tenant you're consenting for.

Run the assessment before you decide

It's read-only, and it tells you the real size of the job — including the archives that usually double it.