MBX (Eudora)
TOC · EudoraEudora'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
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.
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.
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.