---
title: "MBX (Eudora) — Glossary — Mbox Viewer"
description: "Eudora's mailbox file: plain mbox under a different extension, paired with a .toc index file. Readable today with no conversion — but its attachments were stored outside the mailbox."
url: https://mboxviewerpro.com/glossary/mbx/
language: en
source: Mbox Viewer
---

[Mbox Viewer](https://mboxviewerpro.com/)  [Glossary](https://mboxviewerpro.com/glossary/)  MBX (Eudora)

# MBX (Eudora)

TOC · Eudora

Eudora's mailbox file: plain mbox under a different extension, paired with a .toc index file. Readable today with no conversion — but its attachments were stored outside the mailbox.

Eudora, the email client that dominated the early internet, stored each mailbox as a plain-text file with an .mbx extension: messages one after another, each starting with a "From " envelope line, exactly like MBOX. Beside it sat a .toc file holding Eudora's own table of contents — message positions, read state, sizes. The .toc is not needed to read the mail; it can be ignored or lost without consequence.

One quirk surprises people opening these files today: Eudora usually wrote the envelope line as "From ???@???" instead of a real address, filling in a placeholder. It looks alarming and changes nothing — the real sender is in the From: header, where any parser that reads headers rather than guessing from the envelope will find it.

The genuine gap is attachments. Eudora detached them, writing each one into a separate attachments folder and leaving a line in the message body reading Attachment Converted: followed by a path. A recovered .mbx therefore shows attachments as references, not files, unless that folder was kept too — so copy the whole Eudora directory, not just the mailboxes. Mbox Viewer registers .mbx (and .mbs) alongside .mbox, so these files open with a double-click, no renaming required.

## Related terms

[

MBOX

A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive.

](https://mboxviewerpro.com/glossary/mbox/)[

mboxrd / mboxo

The MBOX family's variants, which differ in how they protect body lines that begin with "From ". mboxrd escapes them reversibly; mboxo does not; mboxcl and mboxcl2 use a Content-Length header instead.

](https://mboxviewerpro.com/glossary/mboxrd/)[

Attachment

A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open.

](https://mboxviewerpro.com/glossary/attachment/)

[Back to the full glossary](https://mboxviewerpro.com/glossary/)

## Read your MBOX files on Mac and Windows

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