Outlook PST Size Fix & Auto-Mount

A one-click batch tool that raises the Outlook PST size limit to 512 GB and automatically mounts any PST in its folder. USB-portable — built for IT support desk use.

The Problem

When migrating users or recovering email archives, Outlook's default PST size cap (~50 GB) blocks large .pst files from opening correctly, and manually mounting each PST through Outlook's UI is tedious when you're processing many of them across machines. IT support needed a repeatable, zero-install tool they could carry on a USB stick.

The Solution

A single setup.bat that:

1. Raises the size limit — sets the MaxLargeFileSize registry key to support up to 512 GB PST files (Outlook 365 / 2016+)
2. Auto-mounts — detects any .pst file in the same folder as the script and adds it to the current Outlook profile
3. Launches Outlook — so the mailbox is immediately accessible

How to Use

1. Copy to USB — copy setup.bat and this README.md to your USB drive.
2. Add the PST — place your large .pst file in the same folder as setup.bat.
3. Run — double-click setup.bat.

How It Works

Step	Action
Registry update	Sets MaxLargeFileSize to the 512 GB value in the current user's Outlook registry hive
Auto-detect	Scans the script's own folder for .pst files
Mount	Adds the detected PST to the active Outlook profile via the Outlook automation interface
Launch	Starts Outlook so the mailbox is visible immediately

Tech Stack

Windows Batch · Windows Registry · Outlook COM automation

Troubleshooting

• "Failed to mount PST" — ensure Outlook is installed and you're logged in to a profile.
• Security warning — you may need to "Run as Administrator" if registry keys are locked, though this usually runs fine as a standard user for the current user's registry hive.

License

MIT.