If an OST won’t convert to PST, first stabilize the OST and source environment, then use native export paths; only move to recovery or dedicated converters when Outlook/Exchange access is impossible or the OST is corrupt.​

When conversion fails

  • Typical blockers are a corrupt OST, orphaned profile, missing Outlook/Exchange, or insufficient export permissions; treat these as separate scenarios to avoid data loss or partial exports.​

Quick decision tree

  • You have Outlook + healthy profile + server access: use Outlook export or Exchange mailbox export.​
  • You have Exchange on‑prem, and the mailbox is available: export with New-MailboxExportRequest/EAC to PST.​
  • Outlook unavailable, profile orphaned, or machine decommissioned: consider offline parsing of OST with a converter; validate chain-of-custody for compliance.​
  • OST appears corrupt: attempt Inbox Repair (scanpst) first; scanost is legacy and no longer present in modern Outlook.​

Pre-flight checks

  • Verify OST health: run the Inbox Repair Tool (ScanPST.exe) against the OST; it repairs index-level issues that can block export, and is supported in current Outlook versions.​
  • Confirm mailbox accessibility and permissions if exporting from Exchange; assign the Mailbox Import Export role and a UNC target share accessible to the Exchange server.​
  • Ensure target disk space on the PST share is sufficient; exports create full copies and can temporarily duplicate space.​

Method 1: Export mailbox to PST from Exchange (no Outlook)

  • Best for: You can access the live mailbox on Exchange Server 2013+; it avoids dealing with local OST entirely.​
  • Steps (PowerShell):
    • Assign the Mailbox Import Export role to an admin role group if not present; the export cmdlet requires this role.​
    • Create a UNC share, grant Exchange Trusted Subsystem write access, e.g., \Server\PST_Export.​
    • Run: New-MailboxExportRequest -Mailbox user@domain -FilePath “\Server\PST_Export\user.pst” and monitor with Get-MailboxExportRequest.​
    • Use IncludeFolders/ExcludeFolders or ContentFilter to scope folders or dates if partial export is required.​
  • Steps (EAC):
    • In EAC: Recipients > Mailboxes > select user > More options > Export to a PST file; specify UNC path and start the request.​
  • Notes: This path does not require Outlook on an admin workstation and succeeds even if the client’s OST is problematic, as it reads from the server copy.​

Method 2: Export with Outlook (profile online and healthy)

  • Best for: Admin workstation with Outlook where the profile still connects to the mailbox; uses server-side sync to materialise data.​
  • Steps:
    • In Outlook: File > Open & Export > Import/Export > Export to a file > Outlook Data File (.pst) > choose folders; finish wizard to generate PST.​
    • For large mailboxes, split by date ranges or folder groups to avoid UI timeouts and PST size growth issues.​
  • Notes: Requires Outlook and a working profile; if the profile is orphaned (no server), the Outlook export will not load full content beyond cached data.​

Method 3: Export OST contents without Outlook (tool-agnostic)

  • Reality check: Windows and Exchange provide no built-in CLI to read an orphaned OST; you need an OST parser to extract to PST/EML/MBOX when Outlook/server are unavailable.​
  • What to look for in a converter:
    • Reads orphaned/inaccessible OSTs, preserves metadata, attachments, and supports selective export by folder/date.​
    • Supports formats beyond PST (EML/MSG/MBOX/PDF) for eDiscovery and staged migrations.​
    • Works without Outlook installed, and can preview items for validation before export.​
  • Workflow (generic):
    • Copy the OST to a forensic working directory; avoid writing to the original machine to prevent hash changes.​
    • Load OST in the converter, review the tree, and export to PST with filters; validate by mounting PST in Outlook or in a viewer.​
  • Caveat: Vet tools in a lab, especially for very large OSTs and multilingual content; enforce logging and checksums for audit.​

Repair the corrupt OST before export

  • Use the Inbox Repair Tool (ScanPST.exe) on the OST; current Microsoft guidance documents recommend using ScanPST for both PST and OST corruption remediation in modern Outlook.​
  • Legacy ScanOST is deprecated; references exist for older versions only and require Exchange connectivity—don’t rely on it in Office 2010+ estates.​
  • After repair, reattempt Outlook export or Exchange export; if the OST remains unreadable, fall back to mailbox export from the server or an offline converter.​

Exchange-side export tips

  • Permissions: Confirm the account has the Mailbox Import Export role and the Exchange Trusted Subsystem has write access to the UNC share, or the request will queue/fail.​
  • Scope and filtering: Use IncludeFolders/ExcludeFolders or ContentFilter for dates/senders to reduce PST size and speed up exports.​
  • Monitoring: Use Get-MailboxExportRequest/Remove-MailboxExportRequest to manage and clean up completed jobs.​

Handling special scenarios

  • Decommissioned or reimaged laptops with only OST left: You cannot “reattach” OST to a new profile; proceed with offline OST parsing/export as in Method 3.​
  • Litigation hold/eDiscovery: Prefer server-side export to preserve chain-of-custody and include hold content; document role assignments and UNC permissions in your case notes.​
  • Very large OST (>50 GB): Chunk exports by folder/date; confirm target PSTs stay under policy limits; server-side export handles scale better than desktop Outlook.​

Step-by-step: convert OST to PST without Outlook

  • If the mailbox is available on Exchange, run New-MailboxExportRequest to a UNC share and verify output; Outlook is not required on the admin machine.​
  • If the mailbox is unavailable and only the OST exists: use an OST-to-PST converter that works without Outlook; load OST, preview, export to PST, then validate results in a clean Outlook profile or viewer.​
  • If OST is corrupt: attempt ScanPST on the OST, then retry the chosen export path; if it still fails, pivot to Exchange export (if mailbox exists) or a robust converter with recovery capabilities.​

Checklist for IT admins

  • Confirm what you have: live mailbox vs only OST; Outlook presence; Exchange permissions; corruption status.​
  • Pick the lowest-risk path first: Exchange export, then Outlook export, then offline converter.​
  • Always validate PST integrity: open in Outlook and spot-check folders and counts; retain logs of export commands and hashes for audit.​

Common errors and fixes

  • New-MailboxExportRequest not recognized: ensure Exchange Management Shell is used and the role is assigned to the operator.​
  • Access denied to PST path: grant Exchange Trusted Subsystem write permissions to the UNC share.​
  • Export stuck in queue: verify mailbox health, database performance, and share connectivity; consider scoping with filters to reduce load.​

This playbook prioritizes native, auditable exports and uses offline parsing only when Outlook/Exchange access is unavailable, aligning with a minimal-risk, compliance-first approach for India/US enterprise environments.