How to migrate email from OST to PST — methods, pitfalls and the best software choices

Migrating mailbox data from an Outlook .ost (Offline Storage Table) file to a .pst (Personal Storage Table) file is a common task for IT admins, consultants and power users. OST files are cached copies of mailboxes tied to an Exchange, Outlook.com or Office 365 account; PST files are standalone archives you can import into any Outlook profile. You might need OST → PST migration when you’re moving mailboxes between accounts or machines, recovering mail from an orphaned OST, or preparing data for long-term archiving or third-party migration tools. Microsoft documents the difference and explains the built-in export flow for PSTs.

Below I’ll walk through the core approaches (manual and automated), common pitfalls, and the most widely used third-party tools — what they do, when to use them, and a few practical tips.

Manual options (when you should try these first)

1. Use Outlook’s Import/Export (Export to a PST)
   If the mailbox is still connected to the profile on the machine (i.e., the OST is not orphaned and Outlook can access the mailbox), the simplest method is Outlook’s File → Open & Export → Import/Export → “Export to a file” → PST. This preserves folder structure and most item properties. It’s the safest first step because it uses Outlook’s own APIs.
2. Archive / drag-and-drop
   For small sets of folders, you can create a new PST in Outlook and drag folders or messages into it. That’s manual and slow for lots of data but useful for selective exports.
3. Recreate the account + copy
   If your goal is migration between accounts on the same machine, add the target account/profile to Outlook and copy mailboxes directly between profiles (requires both accounts accessible in the same Outlook instance).

When manual fails: the OST is corrupted, the original Exchange/Office 365 account is gone, or you don’t have credentials to attach the OST to an Outlook profile. In these cases you need specialized conversion software.

Why use third-party OST→PST tools?

• They can read orphaned / offline / corrupted OST files and extract mailbox items when Outlook won’t open the file.
• They support bulk conversion and filters (date ranges, folders).
• They often convert to multiple target formats (PST, EML, MSG, MBOX, Office 365).
• Many provide a preview to verify data before exporting and recovery options for deleted items or metadata preservation.

Reputable vendors also document compatibility with recent Outlook/Windows versions and provide trial builds to validate results before purchase.

Leading OST→PST tools

Below are the names you’ll keep seeing in IT forums and vendor comparisons. I list core strengths and notable limitations.

1. SysTools OST to PST Converter

Strengths: Mature product with multiple scan modes (normal/advanced), support for large or corrupted OSTs, selective export and filters, and ability to recover deleted items. Good for enterprise usage and orphaned OSTs. Limitations: Licensing per-seat and demo limitations (preview only / limited items saved).

2. Kernel for OST to PST

Strengths: Converts OST to PST and to cloud/other mail platforms (Office 365, Exchange, Gmail), supports bulk files, and provides a save snapshot/resume feature for long jobs. Well suited for IT teams doing migrations to cloud services. Limitations: full functionality is paid; trial versions often limit the number of items per folder that can be exported.

3. Stellar Converter for OST

Strengths: Fast scanning, good recovery of mailbox items and attachments, and a clear preview interface. Often recommended when dealing with severely corrupted OSTs. Limitations: commercial product — evaluate with the trial to confirm your items are recovered intact.

Practical advice and gotchas

• Always work on copies: copy the OST file before using any tool. Don’t run conversions on the original unless you have a backup.
• Check item limits on trials: many vendors let you preview but only export a limited number of items per folder in trial mode (commonly 25 items/folder). Use the trial to confirm recoverability before buying.
• Verify metadata: ensure the tool preserves To/From/Date/attachments and MAPI properties you care about (calendar recurrence, categories, flags).
• Large OSTs: choose a tool that explicitly supports large/unlimited file sizes and multi-threaded processing if you’re converting many gigabytes.
• Corruption handling: advanced scan modes (deep scan, rebuild) help recover data from damaged OSTs — but verify results by previewing items before export.
• Legal/compliance: if you are migrating regulatory archives, consider the chain-of-custody and produce verified exports (hashes, logs) where required.

Recommended workflow (practical step-by-step)

1. Make an exact copy of the OST (File Explorer) and work on the copy.
2. If Outlook can open the mailbox, try the native Export to PST first (fastest, safest).
3. If export isn’t possible, install a reputable converter trial (SysTools/Kernel/Stellar are common choices) and use the preview to confirm items.
4. Export to PST (or to Office 365/Exchange if you’re migrating to cloud). Use filters to keep file sizes reasonable.
5. Open the resulting PST in Outlook to validate folders, attachments and calendar items.
6. Archive or import into the target profile as required.

Final thoughts

OST→PST migration is a solved problem most of the time — native Outlook features handle connected profiles, and mature third-party tools cover orphaned or corrupted OSTs. The right choice depends on scale (single mailbox vs bulk migration), file health (healthy vs corrupted), destination (local PST vs Office 365/cloud), and compliance needs. Try a free trial, validate with a few mailboxes, and pick a vendor that documents compatibility with your Outlook/Windows versions and provides reliable previews and logs. For Microsoft’s official guidance on PST export and an explanation of OST vs PST, see Microsoft Support.