When Harrington Property Group completed its acquisition of Coastal Realty in early 2025, IT Manager Marcus had exactly 90 days to consolidate two Microsoft 365 tenants into one. Coastal Realty's 140 staff were joining. Their SharePoint held eight years of property listings, settlement documents, agency agreements, and deal-stage folders. Not a single file could go missing.
Two Microsoft 365 tenants, one tight deadline
Harrington ran a mature Microsoft 365 environment: SharePoint Online for document management, Teams for internal communications, and a structured set of site collections organised by state and property type. Coastal Realty had a smaller but equally real tenant: fewer sites, but a large volume of historical transaction documents that agents and conveyancers still referenced regularly for ongoing settlements.
A business acquisition does not automatically merge two Microsoft 365 tenants. Each organisation is a separate Azure Active Directory with its own user accounts, groups, and SharePoint sites. Moving content between them is a cross-tenant migration, not an internal copy. Files cannot simply be dragged between portals; metadata, version history, and content types must all be preserved or the resulting library is unusable.
Marcus's situation involved four main document libraries on the Coastal side:
- Listings - active and completed property listings with up to 40 versions per listing document
- Settlement Files - legally sensitive, with strict metadata fields (settlement date, property ID, purchaser reference)
- Agency Agreements - contracts with external parties, some still under active terms
- Marketing Assets - high-resolution images and brochures, large individual file sizes
The content weighed in at roughly 220 GB before version history. With versions included, the actual transfer volume was closer to 480 GB.
What a manual approach would have looked like
Marcus scoped out three alternatives before settling on a tool-based migration.
SharePoint Migration Tool (Microsoft SPMT) supports intra-tenant migrations well but has limited support for cross-tenant scenarios and does not preserve custom metadata column values on file migration. Settlement Files in particular relied on five custom metadata columns that would need re-population manually if SPMT dropped them.
PnP PowerShell scripting could handle the metadata issue if written carefully, but the script development, testing, and error-recovery work for 480 GB of content across four libraries was estimated at two to three weeks of dedicated developer time. Managing throttle-safe batch operations, mapping Coastal's users to Harrington's Entra ID accounts, and handling large files reliably added more complexity than the team had capacity for inside the 90-day window.
Manual download and re-upload Marcus ruled out immediately. No metadata, no version history, no audit trail: every settlement file would look as though it was created on migration day by whoever ran the upload.
"I needed something that would handle the metadata mapping and run overnight without me watching it. We had compliance obligations on the settlement files that meant version history wasn't optional." Marcus, IT Manager, Harrington Property Group
Planning the cross-tenant SharePoint migration
Marcus used ShareMaster's Clone Master for the cross-tenant migration. The pre-migration planning phase took two days and covered four areas.
Inventory and size assessment
Before moving anything, Marcus used ShareMaster's Report Master to export a file inventory for each Coastal library: file count, total size (current files and versions separately), column values, and last-modified dates. This gave him an accurate picture of what he was transferring and identified two libraries where version counts were inflated by automated check-in processes that had run for years without a trim.
The Marketing Assets library had no custom metadata worth preserving in column form, just file content and folder structure. The Listings library had three custom columns; Settlement Files had five. Marcus documented the column names and data types so he could verify they mapped correctly in the destination tenant before the main run.
Version cleanup before migration
Two of the four libraries had version histories that were adding significant transfer weight without adding compliance value. Marcus used Space Master's Version Trimmer to reduce those libraries to the 50 most recent major versions per file before the migration run. That cut the effective transfer volume from 480 GB to 310 GB, reducing migration time by roughly one third.
Destination site setup
On the Harrington tenant side, Marcus created matching site collections and document libraries with the correct column definitions before Clone Master began transferring content. Clone Master maps column values during migration, but the destination columns need to exist first. A 30-minute setup step saved potential column-mismatch errors mid-run.
Read the step-by-step guide to migrating a SharePoint site to another tenant
Running the cross-tenant migration
Marcus ran Clone Master from a workstation connected to both tenants simultaneously. Clone Master authenticated to the Coastal source tenant and the Harrington destination tenant, then transferred library content file by file, preserving:
- Custom metadata column values for all five Settlement Files columns and all three Listings columns
- Version history for files where versions existed on the source (subject to the pre-migration trim already applied)
- Folder structure within each library
- File creation and modification timestamps (preserved as metadata on the destination)
The Listings and Settlement Files libraries ran overnight. The Agency Agreements library completed in under two hours. Marketing Assets, which had large individual files, was processed in a separate run with a higher per-file timeout configured.
SharePoint's request throttling kicked in twice during the overnight run on Settlement Files. Clone Master handled the back-off automatically each time and resumed without manual intervention. Marcus found a clean completion report in the run log the next morning - no failed items.
What transferred and what needed manual follow-up
| Content element | Transferred automatically by Clone Master | Required manual follow-up |
|---|---|---|
| File content and folder structure | Yes | No |
| Custom metadata column values | Yes | No |
| Version history (post-trim) | Yes | No |
| SharePoint permissions (unique grants) | Structure migrated; user accounts re-mapped | Yes - Coastal user accounts dissolved; Harrington accounts needed assigning to destination groups |
| Shared links (external sharing) | No - source-tenant links become invalid | Yes - any active external sharing links required recreating in the destination tenant |
| Views and list formatting | Default views only | Yes - custom views recreated manually (approximately 3 hours) |
Permissions were the largest manual task. Coastal Realty's user accounts ceased to exist once the tenants separated in Entra ID. Marcus used ShareMaster's Shared Links & Permissions tool to audit the destination libraries after migration, identifying where access grants were incomplete or broken. He then assigned the correct Harrington accounts to each site and library manually, using a Report Master permission matrix export as his guide. The process took a full day but was straightforward once the audit gave him a clear picture of the gaps.
Outcome: what 90 days produced
All four libraries migrated completely within the 90-day window. Settlement Files arrived with metadata intact and version histories preserved, satisfying the compliance requirement. The pre-migration trim reduced total storage consumption by 170 GB compared to a raw migration, which kept Harrington's storage pool within existing quota limits without a licence upgrade.
Coastal Realty's staff were onboarded to the Harrington tenant in week eight. By the time they needed their historical documents, the libraries were live on the Harrington SharePoint and searchable in their new accounts.
Marcus noted two lessons for the next acquisition: set up destination columns before starting any migration run, and plan two full days for permission reassignment after the content transfer completes. Both steps are predictable once you have been through the process once.
Learn more about Clone Master's cross-tenant migration capabilities