# Mbox versus pst: why Outlook will not open your mbox ## What are mbox and pst, really? If you have ever exported your email or stumbled on an old mailbox, you have probably met two file types: mbox and pst. Both are ways to store email inside a file, but they come from two different worlds and do not speak the same language. An **mbox file** is, at its core, one large text file in which every message in a folder is stored one after another. Each message starts with a line beginning with the word From, followed by the complete email: the sender, the subject, the body and the attachments. The format is old, simple and open. Mail programs such as Mozilla Thunderbird and Apple Mail (macOS Mail) have long used mbox to keep your folders. Google Takeout, the service that lets you download your Gmail, also hands your mail over as mbox. A **pst file** (Personal Storage Table) is the format used by Microsoft Outlook. It is not a plain text file but a kind of small database inside a single file. It holds not only your emails, but also your calendar appointments, contacts, tasks and folder structure, all in a closed, binary shape that Microsoft designed itself. ## Why Outlook will not open your mbox The short answer: Outlook is built to understand pst (and the related ost), and nothing else. It simply does not know the mbox format. When you click Open in Outlook, the file dialog only shows pst files. Your mbox file is not listed at all, or it is refused. This is not a mistake or a missing button, it is a fundamental difference: - **Mbox is open and flat.** Messages sit as readable text one after another. Any developer can build a reader for it. - **Pst is closed and structured.** It is a binary database with its own layout, once meant for Outlook alone. - **The internal logic differs.** Pst keeps calendar, contacts and tasks; mbox keeps only the mail messages of a folder. Because the two formats are built so differently, Outlook cannot simply read an mbox file. A translation has to happen first, a conversion from mbox to pst, before Outlook can deal with it. :::info title="It does not work the other way around either" Just as Outlook does not read mbox, Thunderbird or Apple Mail will not open a pst file directly. Each program prefers to stick to its own format. If you want to move mail from one program to another, a conversion step is almost always needed. ::: ## What ways are there to read mbox anyway? The good news is that you are not stuck. There are three practical routes, each with its own upside and downside. ### 1. Import into a program that understands mbox Thunderbird (free) can use mbox folders directly, often with a small helper add-on for importing. Apple Mail on a Mac has a built-in option, Import Mailboxes, that pulls in mbox files. This is handy when you want to keep using the mail in your everyday mail program. ### 2. Convert to pst for Outlook If you really need the mail inside Outlook, you have to turn the mbox file into pst. That is done with conversion software. The downside: such tools are often paid, you load your entire mailbox into a third-party program, and online converters ask you to upload sensitive mail to a stranger's server. For private messages that is not a comfortable idea. ### 3. Read it in your browser, locally and without the cloud Often you do not want to import an mbox file at all, you just want to open it quickly, search it and view or save a few messages. For that, an mbox reader is ideal. Mbox Viewer by Cloud Captains is exactly such a reader, and it runs as a Chrome extension entirely on your own device. You drag the file onto the window and your mail appears at once, with a list on the left and the message on the right, just like Gmail or Thunderbird. :::tip title="Privacy first" Mbox Viewer works 100 percent locally and offline. Nothing is uploaded, there are no servers and no telemetry. Your mail stays on your own device, stored inside the browser. That makes it a safe choice for sensitive or confidential messages. More at https://mbox-viewer.online ::: ## Opening mbox in your browser, step by step :::howto title="View an mbox file with Mbox Viewer" 1. Install Mbox Viewer by Cloud Captains from the Chrome Web Store and open the extension. 2. Drag your .mbox or .mbx file from your file explorer or Finder onto the viewer window. 3. Wait for the messages to appear in the list on the left. A .mbox.gz from Google Takeout is unpacked automatically. 4. Click a message to read it on the right. Switch between the Preview, Raw and Forensic tabs. 5. Use the search box to filter quickly, for example with from:name or subject:invoice. 6. To keep a message, export it as PDF, .eml, .html or .mbox using the export button. ::: Besides .mbox and .mbx, the viewer also opens .eml and .emlx (Apple Mail), .msg (Outlook), Maildir folders and .mbox.gz. That lets you view different mail sources in one and the same window without having to open a separate program for each format. :::warn title="Be careful with online converters" Free online mbox-to-pst converters ask you to upload your mail file. By doing so, you hand your entire email history to an unknown party. Never do this with business, legal or personal mail. Choose a local solution instead, one that does not take your file off your device. ::: ## Which route suits you? - **You want the mail permanently in your daily mail program:** import it into Thunderbird or Apple Mail. - **It really has to be in Outlook:** convert to pst, preferably with software that runs locally. - **You only want to read, search, check or save a few messages:** open the file locally in your browser with Mbox Viewer. For most people who rediscover an old mbox file, that last route is the fastest and safest. You do not have to install anything in your mail program, you do not give your privacy away to the cloud, and you have your mail on screen within seconds. :::faq ### Why can Outlook not open mbox? Outlook is built around its own formats, pst and ost. It does not know the mbox format and offers no built-in way to read it. You have to convert the mbox file to pst first before Outlook can show the messages. ### What is the difference between mbox and pst? Mbox is an open, flat text format in which the messages of a folder are stored one after another, used by Thunderbird and Apple Mail. Pst is a closed, binary database from Microsoft that, besides email, also keeps calendar, contacts and tasks, used by Outlook. ### Can I read an mbox file without installing anything in my mail program? Yes. With Mbox Viewer by Cloud Captains you open an mbox file directly in Chrome by dragging it onto the window. You do not have to import anything into Thunderbird or Outlook, and your mail stays local on your device. ### Is it safe to open my mbox in the browser? With Mbox Viewer it is. The extension works entirely locally and offline, without uploads, servers or telemetry. Your mail is only stored on your own device. That is safer than an online converter, which sends your file to an external server. ### How do I open mbox mail from Google Takeout? Google Takeout delivers your Gmail as a .mbox.gz file. Just drag that file onto Mbox Viewer and it is unpacked automatically, so your messages appear in the list right away. ### Can I still move my mbox mail to Outlook later? You can, but that requires a conversion to pst using separate software. If you only want to view the messages or keep a selection, no conversion is needed and a local viewer is simpler and more privacy-friendly. :::