What is the TOC file format?
A .toc file is a table of contents file that indexes the messages stored within the Eudora mail program. Rather than holding message content itself, the .toc acts as a binary index paired with a companion .mbx mailbox file of the same name - recording each message's byte offset, length, and key metadata so Eudora can navigate the mailbox quickly.
The Eudora mail program was developed by QUALCOMM and ran on Windows and Mac OS. The messages listed in a .toc file can be browsed and opened using the Eudora client, which supported Windows and Mac OS (Classic and early OS X). QUALCOMM discontinued classic Eudora development in 2006; a later open-source successor used .mbox format instead of .toc files.
Because the .toc is purely an index, Eudora can regenerate it automatically if the file is missing or damaged by scanning the companion .mbx. The actual email content lives in the .mbx, not the .toc.
Some of the common .toc files in a Eudora mail profile are:
in.toc- lists the Inbox messagesout.toc- lists the Outbox messagesjunk.toc- lists the Junk/Spam messagestrash.toc- lists the Trash messages
To migrate old Eudora mail to modern clients, the data of interest is the .mbx file, which can be converted to .eml or .pst format using tools such as Mozilla Thunderbird with the ImportExportTools NG add-on or dedicated conversion utilities.
Security & safety
RISK: LOWA Eudora .toc is an inert binary index and carries no executable code, so the file itself is harmless. The only real considerations are practical: it is useless without its matching .mbx, and old email archives may contain attachments whose own risk should be judged separately once you open the messages. When recovering legacy mail, work on copies. (For the unrelated World of Warcraft .toc, only ever install addons from trusted sources, since they ship executable Lua - but that is a different file format.)
Format details
in a nutshell- World of Warcraft addon manifest (.toc) - A plain-text metadata file listing an addon's name, version, dependencies and .lua/.xml files - by far the most common .toc seen today, but a different format from the Eudora index.
- Disc-image cue/TOC (cdrdao, Brasero) - A text table-of-contents describing CD tracks for burning tools like cdrdao and Brasero.
- LaTeX / book table of contents (.toc) - An auto-generated plain-text aux file LaTeX writes to build a document's table of contents.
Programs that open TOC files
Windows3 apps
Eudora (classic, legacy)
Free If you still run classic Eudora, it opens its own mailboxes automatically. Discontinued in 2006 - use only on legacy systems; for migration prefer a converter below.
Aid4Mail / Eudora-to-* converters
Paid Point the converter at the Eudora mailbox folder to migrate .mbx (and its .toc) into mbox/PST/EML for Outlook or Thunderbird. The practical way to read old Eudora mail.
Mozilla Thunderbird (with ImportExportTools NG)
Open-source Import the Eudora .mbx as mbox via the ImportExportTools NG add-on; the .toc index is not needed. Free route to view old messages. 
macOS1 app
Mozilla Thunderbird (with ImportExportTools NG)
Open-source Import the Eudora mailbox (.mbx → mbox) to read messages; the .toc is rebuilt/ignored. Free. 
Linux1 app
Mozilla Thunderbird (with ImportExportTools NG)
Open-source Import the Eudora .mbx as mbox to view the actual mail. The .toc index has no standalone use. Technical details
deep spec| File role | Binary mailbox index - records the position and metadata of each email inside the paired .mbx; the .toc does not store message content |
| Companion file | Always paired with a same-named .mbx mailbox file (e.g., in.toc pairs with in.mbx); a .toc file is meaningless without its .mbx |
| Per-message record fields | Status flags, sender address, subject line, date/time, byte offset into the .mbx, and message length in bytes |
| Encoding | Proprietary binary; internal structure is undocumented and not publicly specified by QUALCOMM |
| Byte order | Platform-dependent - Mac OS and Windows builds of Eudora used different byte ordering in the binary records |
| Compression | Uncompressed binary records; all fields stored as raw binary data |
| MIME type | application/octet-stream |
| File signature | No published magic bytes or header signature; identified by its .toc extension and filename context alone |
| Typical file size | A few kilobytes to several megabytes, scaling proportionally with the number of messages indexed |
| Standard filenames | in.toc (Inbox), out.toc (Outbox), junk.toc (Junk/Spam), trash.toc (Trash) |
| Supported platforms | Windows (Eudora 1 through 7); Mac OS Classic; early Mac OS X |
| Self-healing index | Eudora automatically rebuilds a missing or corrupted .toc by scanning the companion .mbx file |
| Migration role | Discarded during email migration; the .mbx carries the actual messages for conversion to .eml or .pst |
| Internal version | Format version tied to Eudora release; not publicly documented; changed incrementally across Eudora 1 through 7 |
| Released | Early 1990s, with the Eudora email client (QUALCOMM commercialized it from 1993) |
| Latest version | Tied to Eudora; last classic release Eudora 7.x (2006); QUALCOMM discontinued Eudora development in 2006 |
TOC conversions
Community Q&A
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