---
title: "How to Open a Thunderbird MBOX File on Windows — Mbox Viewer"
description: "Thunderbird on Windows stores your mail as standard mbox files with no extension, tucked inside your profile folder. Here's how to find and read them with Mbox Viewer on Windows 10 and 11."
url: https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-windows/
language: en
updated: 2026-06-18
source: Mbox Viewer
---

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

# How to Open a Thunderbird MBOX File on Windows

Thunderbird on Windows stores your mail as standard mbox files with no extension, tucked inside your profile folder. Here's how to find and read them with Mbox Viewer on Windows 10 and 11.

PublishedJune 18, 2026

Mozilla Thunderbird has stored email in the open [**mbox**](https://mboxviewerpro.com/glossary/mbox/) format for over twenty years, so your Thunderbird mail on Windows is *already* in a format any standard reader can open. Two things trip people up on a PC: the mailbox files have **no extension**, and they’re hidden away inside the `AppData` folder that Windows keeps out of sight. This guide shows you exactly where to look and how to read them with Mbox Viewer.

> Mbox Viewer for Windows is available on the [**Microsoft Store**](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) — install it and follow the steps below.

## Where Thunderbird hides your mail on Windows

Each mailbox (Inbox, Sent, your custom folders…) is a single mbox file inside your Thunderbird profile:

```
%APPDATA%\Thunderbird\Profiles\<random>.default-release\Mail\Local Folders\
```

The quickest way there: press `Win + R`, paste `%APPDATA%\Thunderbird\Profiles` and hit Enter — File Explorer opens right inside it. (`%APPDATA%` expands to `C:\Users\<you>\AppData\Roaming`, which is hidden by default, so the `Win + R` shortcut saves you from un-hiding folders.)

Inside `Mail\Local Folders\` you’ll see files named `Inbox`, `Sent`, `Archives` and so on **with no extension**, each paired with a `.msf` file of the same name. The `.msf` files are just Thunderbird’s index — ignore them. The extension-less files are your actual mail, in standard mbox format. Mail tied to an IMAP account lives under an `ImapMail\` folder instead.

## Option 1: export with ImportExportTools NG (recommended)

The free [ImportExportTools NG](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) add-on is the tidiest route and works the same on Windows as anywhere:

1.  In Thunderbird, install **ImportExportTools NG** from the Add-ons Manager.
2.  Right-click any folder → **ImportExportTools NG → Export folder**.
3.  Choose a destination — you get a proper `.mbox` file.
4.  Open it with **Mbox Viewer**: double-click in File Explorer or drag it onto the window.

## Option 2: open the mailbox file directly

No add-on needed — Mbox Viewer reads Thunderbird’s extension-less files as-is:

1.  **Close Thunderbird** so the files aren’t locked.
2.  Open the profile folder with the `Win + R` trick above and go into `Mail\Local Folders\`.
3.  **Copy** the mailbox you want (e.g. `Inbox`) to somewhere easy like your Desktop. Always copy — never move the original, or Thunderbird loses track of it.
4.  In Mbox Viewer, use **File → Open** and pick the copy. No need to add a `.mbox` extension.

## What you can do once it’s open

You can [search with the full query syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), follow threaded conversations, preview [attachments](https://mboxviewerpro.com/glossary/attachment/) and export to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text. Mbox Viewer is strictly **read-only**, so your Thunderbird data is never altered. Even a 20-year-old, 30 GB inbox opens smoothly thanks to the [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/). New to the format? Start with [how to open an MBOX file on Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/).

## 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)