---
title: "How to Convert Outlook PST/OLM to MBOX (Mac & Windows)"
description: "Outlook stores mail in PST (Windows) or OLM (Mac), which Mbox Viewer can't open directly. Here's how to convert PST and OLM files to standard mbox — free, step by step — then read them."
url: https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/
language: en
updated: 2026-06-18
source: Mbox Viewer
---

[All guides](https://mboxviewerpro.com/guides/)

# How to Convert Outlook PST/OLM to MBOX (Mac & Windows)

Outlook stores mail in PST (Windows) or OLM (Mac), which Mbox Viewer can't open directly. Here's how to convert PST and OLM files to standard mbox — free, step by step — then read them.

PublishedJune 18, 2026

Microsoft Outlook doesn’t use [mbox](https://mboxviewerpro.com/glossary/mbox/). On Windows it stores everything in a [**PST**](https://mboxviewerpro.com/glossary/pst/) database; Outlook for Mac uses an **OLM** archive. Neither is mbox, so Mbox Viewer can’t open them directly — you convert to standard mbox first, then open the result. This guide covers a free, reliable route for both formats and works on **Mac and Windows**.

## Why convert at all?

PST and OLM are proprietary, single-vendor containers. Converting to the open mbox format frees your mail from Outlook, gives you one portable archive, and lets you read, [search](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) and export it in Mbox Viewer without an Outlook licence or a running mail account.

## Convert a PST file (Outlook for Windows)

The cleanest free method uses **Mozilla Thunderbird** as a bridge — no paid converter required:

1.  Install [Thunderbird](https://www.thunderbird.net/) and the free [ImportExportTools NG](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) add-on.
2.  In Outlook, make sure the mail you want is in a `.pst` (in Outlook: **File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst)**).
3.  In Thunderbird, install the **ImportExportTools NG** add-on, then use its tools (or the Thunderbird import wizard) to bring the PST data into a Local Folder.
4.  Right-click the folder → **ImportExportTools NG → Export folder** to write a standard `.mbox` file.

Prefer a one-step tool? Dedicated **PST-to-MBOX converters** exist for Windows; pick a reputable one, and always work on a *copy* of your PST.

## Convert an OLM file (Outlook for Mac)

OLM is Mac-only and a bit more involved:

1.  In Outlook for Mac, export with **Tools → Export…** to create the `.olm` (work on a copy).
2.  Use an **OLM-to-MBOX converter**, or re-import the OLM into a mail client that can then export mbox (Thunderbird with ImportExportTools NG, as above).
3.  The output is one or more `.mbox` files.

## Open the result in Mbox Viewer

Once you have a `.mbox` file (or an extension-less mbox), open it with **Mbox Viewer**:

-   **Mac:** double-click, drag & drop, or **File → Open**.
-   **Windows:** double-click in File Explorer, drag onto the window, or **File → Open**. (Mbox Viewer for Windows is available on the [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB).)

You get instant browsing, full [search syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), threaded conversations, [attachment](https://mboxviewerpro.com/glossary/attachment/) previews and export to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text — even for multi-gigabyte mailboxes, thanks to the [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/). Everything is **local and read-only**: your converted archive is never modified.

## Related guides

-   [How to open an MBOX file on Mac](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/)
-   [How to open an MBOX file on Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/)
-   [Convert MBOX to CSV, EML and attachments](https://mboxviewerpro.com/guides/convert-mbox-to-csv-and-eml/)

## Open your archive with Mbox Viewer

Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline.

[Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB)