SharePoint Cross-Tenant File Transfer

A PowerShell script for manually triggered file transfer between two SharePoint document libraries across different tenants - including guest/external access scenarios.

Intended scenario

A single or a limited set of users from your organization have been granted guest access to the other's organization SharePoint Site. Work is delegated within your organization across users and/or departments. The script enables your organization to perform automated partial submissions, by mirroring your SharePoint site you have set up for the project.

What it does

• Connects to a source SharePoint site (own tenant) and a destination SharePoint site (external/customer tenant where the user has guest contributor access)
• Performs a differential sync: only files that are new or modified since the last run are transferred - unchanged files are skipped
• Preserves subfolder structure
• Generates a per-session transfer report (plain text, suitable for client handover) saved next to the script files
• Maintains a cumulative debug log in %TEMP% for troubleshooting

Requirements

• Windows with Windows PowerShell 5.1 (built-in, no install needed)
• PnP.PowerShell 1.12.0 - install once with:

  Install-Module PnP.PowerShell -RequiredVersion 1.12.0 -Scope CurrentUser -Force

  Version 1.12.0 specifically is required - newer versions (2.x, 3.x) require PowerShell 7 and will not be found by Windows PowerShell 5.1.

• Contributor access on the destination SharePoint site (guest/external invitation is sufficient)
• No admin rights needed for either installation or execution

Files

File	Purpose
sp-transfer.ps1	Main script
sp-transfer.bat	Launcher - double-click this to run
sp-transfer-config.ps1	Your configuration (never overwritten by upgrades)
sp-upgrade.ps1	Self-updater - downloads latest scripts from GitHub

All files must be kept in the same folder.

Configuration

Edit sp-transfer-config.ps1 (created on first download, never overwritten by upgrades):

$site1Url      = "https://yourcompany.sharepoint.com/sites/Site1"
$site2Url      = "https://customertenant.sharepoint.com/sites/Site2"

$site1Library  = "Documents"   # Display name of the library on Site1
$site2Library  = "Documents"   # Display name of the library on Site2

Library names must match the display name as shown in SharePoint, not the URL segment. Run Get-PnPList | Select-Object Title, RootFolder against the site to confirm the correct name.

Usage

1. Double-click sp-transfer.bat
2. Select mode:
   • 1 - Sync new files only (skip files that already exist on Site2, even if updated)
   • 2 - Normal sync (new and updated files)
   • 3 - Dry run (preview only)
   • 4 - Upgrade
3. Log in to Site1 in the browser window that opens
4. Log in to Site2 in the second browser window (same account, guest access)
5. Wait for the transfer to complete (or preview to finish)
6. Press Enter to close - the report is saved automatically

New files only

Transfers only files that do not yet exist on Site2 (matched by relative path). Files that exist on Site2 are skipped regardless of whether the source copy is newer. Useful when you want to seed the destination with new additions without touching files that may have been edited downstream.

# Via the bat launcher: select option 1
sp-transfer.bat

# Or directly:
.\sp-transfer.ps1 -NewOnly

The report is clearly marked [NEW FILES ONLY].

Dry run

Dry run connects to both sites, compares files, and shows exactly what would be transferred - without downloading or uploading anything. Useful for verifying the diff before committing to a transfer.

# Via the bat launcher: select option 3
sp-transfer.bat

# Or directly:
.\sp-transfer.ps1 -DryRun

The dry-run report is clearly marked [DRY RUN] and lists all files that would be transferred with their [NEW] or [UPDATED] status.

Upgrading

Select option 4 from the bat menu (or run sp-upgrade.ps1 directly). This downloads the latest sp-transfer.ps1, sp-transfer.bat, and sp-upgrade.ps1 from GitHub. Your configuration in sp-transfer-config.ps1 is never modified. A .bak backup of each file is created before overwriting.

Transfer report

Each run produces a timestamped report file in the same folder as the script:

TransferReport_2024-03-24_143210.txt

Example content:

SharePoint Transfer Report
==========================
Date/Time : 2024-03-24  14:32:10
Operator  : firstname.lastname

Files transferred (3)
----------------------------------------
  [NEW]      Data/survey_results.csv
  [UPDATED]  Reports/Q1_2024.xlsx
  [UPDATED]  Reports/Q2_2024.xlsx

Files skipped -- already up to date : 847

Failed (0)
----------------------------------------
  (none)

Authentication

Uses -UseWebLogin (interactive browser popup) for both connections. This handles MFA and cross-tenant guest authentication without requiring app registrations or certificates. Tokens are not cached between runs - the user logs in fresh each time.

Logs

File	Content
TransferReport_<timestamp>.txt	Per-session delivery record, saved next to the script
%TEMP%\SPTransfer_debug.txt	Cumulative debug log across all sessions, for IT troubleshooting

Notes

• Files are transferred one at a time: downloaded to a local temp folder, uploaded to Site2, then the local copy is deleted immediately. Peak local disk usage is one file at a time.
• The script is safe to run multiple times - Add-PnPFile overwrites the destination if the source is newer.
• The update warning (A newer version of PnP PowerShell is available) that appears on connect is harmless and can be ignored.