What OST and PST are

An OST is a cached, offline copy of a mailbox from Exchange, Microsoft 365, or IMAP that Outlook can recreate from the server; Microsoft does not recommend “importing” an OST directly because it’s not a portable backup format and is tied to the original profile and mailbox.
A PST is a portable Outlook Data File designed for export, backup, migration, and archiving of mail, calendar, contacts, and tasks.

Method 1: Export to PST from the configured profile

Prerequisites: The original mailbox profile must open in Outlook and be fully synced; this is the safest, supported path because Outlook can read the OST tied to that profile and export data cleanly.
Steps in Outlook: File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst) → pick top mailbox and include subfolders → choose a save path → Finish; this produces a PST containing emails, calendar, contacts, and more.
Why this works: Outlook reads from the synchronized mailbox/OST and writes a PST, preserving folder structure and items; Microsoft documents this export flow for moving mail between profiles or machines.

After creating a PST, move it to the target PC if needed, then in Outlook use File → Open & Export → Import/Export → Import from another program or file → Outlook Data File (.pst) → select the PST → choose destination mailbox/folders and duplication handling → Finish.
Microsoft also notes the general behavior of opening or importing data files, clarifying that OSTs aren’t meant to be imported while PSTs are designed for this use-case; use PST for portability and restore workflows.

Problem: If the original mailbox/profile is gone, the OST won’t open in Outlook due to profile binding; Outlook cannot directly import an orphaned OST.
Solution: Use a reputable OST to PST converter that can parse orphaned or damaged OSTs, preview content, and export to PST; then import the PST in Outlook via File → Open & Export → Import/Export.

Capabilities to look for: Reading orphaned/inaccessible OSTs, preserving metadata, selective folder export, date/category filters, split large PSTs, and preview before export; these features simplify large or partial recoveries.
Example solutions: Commercial utilities provide bulk conversion, previews, and filters to create clean PSTs when the original profile isn’t available; after export, use Outlook’s Import wizard as in Method 2 to load data into the target profile.

AutoArchive route: Some guides describe archiving items from a live Outlook profile to PST, which can reduce mailbox size and create a PST subset; this still requires a working profile, and export is generally clearer for complete moves.
Repairing data files: If export/import fails due to corruption, run Microsoft’s Inbox Repair Tool (scanpst.exe) against PST/OST as applicable, then retry export or conversion; scanpst is Microsoft’s documented repair utility for Outlook data files.

If Outlook opens the original mailbox: File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst) → select mailbox and subfolders → save PST → move PST → Import in target Outlook.
If only an OST exists and Outlook can’t open it: Use an OST to PST converter to extract data into PST, then Import → Outlook Data File (.pst) in the destination profile as above.

Intent targeting: Title and H1 should address “How to import an OST file into Outlook PST” and include “Export OST to PST” phrasing; include sections for “configured profile” and “orphaned OST” use-cases to match varied user intent.
Step-by-step clarity: Provide numbered steps for Outlook Export and Import wizards, and a decision pathway: “If Outlook opens profile → export; if not → converter tool → import PST” to reduce pogo-sticking and improve dwell time.
E-E-A-T signals: Cite Microsoft support for export/import and repair guidance, and reference recognized utilities for orphaned files; this improves trust and topical authority for migration keywords.

More info- https://www.inspiredatacare.com/convert-ost-to-pst.html