PST files sit on laptops, file shares and USB drives, unmanaged, unsearchable and outside your retention policies. Cloud2Cloud Migrator finds them, works out who owns them and moves them directly into Microsoft 365.
PST files are copies of email that have escaped your mail system. They aren't covered by retention policies, eDiscovery or legal hold until they're brought back into Microsoft 365. Every PST on a laptop or file share is personal data you're responsible for under GDPR and similar laws, and you can't produce, protect or delete it if you don't know it exists.
Microsoft's own PST import service works when you already have a tidy pile of PSTs and know whose they are. Enterprise estates are rarely like that. The hard parts are finding every PST, establishing ownership and moving the data without making more copies along the way.
Most PST tools make you copy files to a staging server first. That duplicates the breach risk and doubles the timeline. We migrate directly from the source location, and the PST never leaves its original disk until its contents are safely in the destination.
Discovery scans file systems at more than 12 million objects per hour and profiles every PST it finds: size, age, location, likely owner and known issues. You see the whole estate before committing to a plan, including orphaned PSTs belonging to leavers, duplicates and files too damaged to open.
From there you decide what to migrate, what to assign to a shared or leaver mailbox, and what to defensibly delete under your retention schedule.
The US Department of Education had 46,000+ PST files, 22 TB in all, spread across 16 file servers, 3 data centres and 10 regional locations. Agents at each site found and analysed the PSTs locally, rules assigned an owner to every file, and each one was cleaned, uniquely named and prepared for Microsoft's import service along with the import mapping file. No file was handled by hand. Read the case study →
"The service has been one of the best from any vendor." — Dimitri Dizna, Dell / U.S. Federal Government
Manpower learned why ownership matters in a ten-user pilot, when two siblings received each other's email. Its 16 TB of PSTs from 300+ UK locations was then assigned by evidence and rules and delivered to Mimecast automatically. Read the Manpower case study →
Once PST data is in Microsoft 365, it falls under your retention policies, eDiscovery and Purview controls. We recommend blocking new PST creation through Group Policy or Intune at the end of the programme, and we provide the discovery reports you need to prove the estate is clean.
Run discovery across file shares, home drives and user profiles first, because that's where most volume sits. Laptops are harder: many only connect to the network occasionally. Plan for repeat discovery passes over several weeks so that files on machines that only appear on Friday afternoons are still found.
Each PST is matched to an owner using Active Directory and analysis of the mail inside the file. A PST in a user's home drive is easy. A PST on a departmental share, named archive_old2.pst, is not. Analysing the content shows whose mail it really is. Files that can't be matched confidently are flagged in the discovery report so your team can make the call.
Discovery shows the estate as it really is: active users' PSTs, leavers' PSTs, copies of the same file in several places, and files too damaged to open. Each category gets a decision. Migrate it, assign it to a leaver or shared mailbox, or defensibly delete it under your retention schedule. Making these decisions before migration keeps the destination clean and the project shorter.
A common pattern is to migrate each PST into the owner's Microsoft 365 online archive, in a folder named after the original file. Users can find their old mail, their primary mailbox stays lean, and the content falls under your retention and eDiscovery policies. Some organisations prefer the primary mailbox for small files. We agree the rule during scoping.
Migration runs directly from each file's original location, with no staging copy. Outlook locks PST files that are open, so communications matter: users should know when their files are being picked up. Per-message checkpointing means an interrupted job resumes from where it stopped, without duplicates.
Once the estate is migrated, stop new PSTs appearing. In Outlook, Group Policy or Intune can stop users adding PST files to their profile and stop existing PSTs from growing. A final discovery pass then proves the estate is clean.
PSTs created by Outlook 2002 and earlier use the old ANSI format, which is limited to 2 GB. Files that hit that ceiling are particularly prone to corruption. Discovery records each file's format and flags oversized or damaged files before migration. During migration, corrupt items are logged and skipped and the rest of the file still moves, so one bad message never strands a whole PST. Password-protected files are reported explicitly so you can decide how to handle them.
Under GDPR, a subject access request covers personal data wherever you hold it, including in PSTs on laptops and file shares. If you can't search those files, you can't answer the request fully, and you can't apply your retention schedule to them either. Moving PST content into Microsoft 365 puts it within reach of Purview eDiscovery, retention and deletion. The migration itself must not create new copies along the way, which is why we migrate directly from source.
Microsoft's import service is fine for a small, known set of PSTs. It doesn't find PSTs across your network, work out who owns them, or avoid staging copies. In enterprise estates, those are the hard parts.
We combine Active Directory integration with analysis of the mailbox content inside the PST, so files are matched to the right user even when they sit on a shared drive or belonged to a leaver.
Our approach is designed to be. PSTs migrate directly from their source location with no intermediate copies, and every action is logged so you can show exactly what happened to each item.
Yes. PST content can be migrated into Microsoft 365, Exchange on-premises, Enterprise Vault or Mimecast.
Corrupt items are logged and skipped so the rest of the file still migrates. Anything that can't be processed is reported explicitly with a reason, so you can decide what to do with it.
The main variables are the number and size of files, how many sit on laptops rather than servers, and Microsoft 365 throttling. Discovery tells you the size of the estate, and a pilot wave gives real throughput figures to plan from.
A common pattern is the owner's online archive, in a folder named after the original file. That keeps the primary mailbox lean while bringing the content under retention and eDiscovery. We agree the rule during scoping.
Book a 30-minute scoping call with the engineers who built the engine. We'll map your sources, volumes and compliance constraints, and tell you honestly where we fit.
Request a scoping call →No sales pitch · No commitment · A technical conversation with the engineers who built the engine