Migrating PST Files
PST files can create clutter risk. Unmonitored, unclassified data scattered across laptops, network shares, and USB drives is a compliance liability waiting to surface in an audit or eDiscovery request. Bluesource finds every PST in your environment and migrates them to a permanent, structured archive.
PST Migration Overview
Organizations move off on-premises Enterprise Vault to Proofpoint for a mix of reasons: reducing the infrastructure and admin overhead of managing an on-prem archive, consolidating security and archiving under one vendor, or meeting compliance requirements that Proofpoint’s journaling and retention model is purpose-built for.
What are PST files?
A PST (Personal Storage Table) is a Microsoft Outlook file format that lets users store mail locally, outside their server mailbox quota. PSTs were never designed for long-term storage: they’re prone to corruption, loss, and theft. Storing PSTs on network shares and removable media increases the risks.
PST vs OST
A PST is different from an OST file: an OST (Offline Storage Table) is Outlook’s local cache for a server-based mailbox, and users never interact with it directly. Only PSTs are the target of a migration project.
PSTs in Microsoft 365
Microsoft 365 gives PST data a permanent, governed, cloud-based home in a user’s primary mailbox or their personal (in-place) archive. Migrating PST files to Microsoft Exchange provides the security, retention, and eDiscovery capabilities PST files were never built for.
PST Migration Is a Compliance Project
PSTs can exist anywhere on your network, holding years of unclassified, unmonitored data. That’s precisely what makes them a liability: content your compliance and legal teams don’t know exists can’t be governed, retained correctly, or produced defensibly.
The files themselves compound the problem: PSTs aren’t encrypted by default, so a lost laptop or a compromised network share can expose everything, with no additional barrier to an attack. Combined with their vulnerability to malware and their tendency to live on the exact kinds of devices most likely to be lost or stolen, PSTs are frequently the weakest link in an otherwise well-governed environment.
Bluesource treats every PST migration as a compliance project first and a data-movement project second. Moving the data without addressing the governance is just relocating the risks.
Importing PST files to the new version of Microsoft Outlook requires users to also have Classic Outlook installed. Bulk importing and removing the Classic Outlook requirement are on Microsoft’s roadmap. Meanwhile, Bluesource works with PSTs without Outlook. Our custom in-house library lets us work with PSTs natively and seamlessly.
What Bluesource Migrates:
- User PST files: from local hard drives, network shares, removable media, and shared PCs.
- Journal PSTs: historical compliance archives, migrated with sender, recipient, and distribution list metadata intact for eDiscovery.
- Orphaned/ownerless PSTs: files belonging to former employees or unidentified owners, resolved through Bluesource’s discovery and reconciliation process rather than left behind.
Locating PST Files
PST files are almost always hiding in two places, and each requires a different approach:
- Network shares. Users routinely drop backup copies onto home drives and team shares. These can be scanned with read-level access and relatively little disruption, producing an initial inventory of file locations, sizes, and last-modified dates.
- Local drives and removable media. Harder to find, and best identified through each user’s Outlook profile so a file can be tied to an actual owner. Shared PCs complicate this further, since multiple Windows and Outlook profiles on one machine all need to be assessed separately.
Expect duplicate copies of the same file across multiple locations. Users keep “just in case” backups, and reconciling those duplicates is part of getting an accurate migration scope.
Not Everything Needs to Migrate
Discovery isn’t just about finding files; it’s about deciding what happens to each one. Some PSTs are genuinely worth retaining and belong in Microsoft 365. Older files may be past your retention window and are candidates for defensible deletion instead. Making that call during Scoping, against your actual retention policy, keeps migrated volume and associated Microsoft 365 storage costs at a minimum.
Establishing Ownership
Ownership resolution is where PST projects commonly stall. It gets progressively harder to determine as you move from a user’s own machine, to a shared PC, to a network share, to a file with no identifiable owner at all. Bluesource’s discovery process is built to resolve ownership at every one of those stages, beyond flagging files as “unknown.”
PST Migration Workflow
Discovery
Every PST is located across network shares, local drives, and removable media, and cataloged by location, size, and last-modified date.
Owenership Resolution
Each file is tied to a current employee, a departed employee, or flagged as ownerless, with a resolution path for each category.
Target + Method Decision
Migration approach and target confirmed, based on data volume, licensing, and hybrid environment considerations.
Migration Execution
PST content is extracted and ingested into Microsoft 365, with full chain-of-custody and message-level auditing throughout.
Validation
Migrated data is reconciled against the source, and the project is formally closed out. Affected users are told what’s happening and any necessary action items.
Prepare your Migration Plan
PST Migration FAQs
Can PST files be migrated straight to Microsoft 365?
Yes. Most organizations migrate PST data into either a Microsoft 365 mailbox or, more commonly, the Microsoft 365 personal archive. The right choice depends on data volume, licensing, and the environment.
Will migrating PSTs disrupt end users?
End-user impact is minimal when handled with a purpose-built migration process. Some approaches even let users keep accessing their PST data during the migration itself, rather than losing access for the duration of the project.
How does Bluesource find PSTs that users don't report themselves?
Discovery scanning covers network shares and, through each user’s Outlook profile, local and removable storage, to avoid relying on employees to self-report files they may have forgotten even exist.
How long does an enterprise PST migration take?
Timeline depends primarily on the number and size of PST files discovered, ownership resolution (which often takes longer than the data copy itself), the target platform, and Microsoft 365 throttling limits. Because of this, Bluesource starts every engagement with a Scoping phase that includes a proof-of-concept, so you get a realistic timeline for your specific environment.
Our Migration Process
Scoping
Your environment is accurately sized
Setup
Software is installed; Test Migration Performed
Reconciliation
Chain of Custody Provided; Validation
Production
Data is continuously moved until complete
