OpenAnyFile
What is a .mbx file?
Mailbox (Eudora / Outlook Express 4) is an email and contacts format developed by Qualcomm / Microsoft. It is usually created by Eudora, early Outlook Express.
mbox-style: messages concatenated, each starting with a 'From ' line.
File details
| Full name | Mailbox (Eudora / Outlook Express 4) |
|---|---|
| Category | Email & contacts |
| MIME type | application/mbox |
| Signature (magic bytes) | 46 72 6F 6D 20 (From ) |
| Developer | Qualcomm / Microsoft |
| Opens with | Email reader |
| Uploaded? | No — read locally in your browser |
How to open a .mbx file
OpenAnyFile routes .mbx files to its email reader, which shows sender, recipients, subject, date and message body.
- Drop your .mbx file on the box above, click it to choose the file, or paste it with Ctrl+V.
- The real format is detected from the file's first bytes — not just its name.
- The file opens in the email reader.
- Use fullscreen for a closer look, check its checksums, or download it back unchanged.
What works — and what does not
Works
Viewing and inspecting: sender, recipients, subject, date and message body. Size, type, signature and checksums are always shown.
Does not work
Editing and saving back. OpenAnyFile is a viewer, not an editor — for changes you still need the original app.
Is it safe to open a .mbx file online?
Here, yes — because nothing is uploaded. Most "online viewers" send your file to their server. OpenAnyFile reads it with your browser's File API and decodes it on your own device, so there is no copy anywhere else. You can check: open your browser's network tab while opening a file — no upload appears.
Questions about .mbx files
Can I open a .mbx file without installing software?
Yes. OpenAnyFile opens .mbx files in your browser using its email reader. You get sender, recipients, subject, date and message body, with nothing installed and no account.
How do I know a file is really a .mbx file?
Check its first bytes instead of its name. A genuine MBX file begins with 46 72 6F 6D 20 (From ). OpenAnyFile shows the detected type, so a renamed file is easy to spot.
Is my .mbx file uploaded anywhere?
No. The file is read locally by your browser and never sent to a server — it even works offline once the page has loaded.
Does it work on phones?
Yes — on Android and iPhone, in any modern browser. You can also install OpenAnyFile as an app.
Related formats
Other formats from the same family:
Format facts checked and page updated on September 25, 2026.