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MSF EML
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Convert MSF to EML

Can you convert MSF to EML?
Verified by Adam B.· reviewed by FE Editorial ·updated Jul 15, 2026
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Is it possible to convert MSF to EML?
No - not a direct conversion.

The .msf file holds only message metadata (subjects, dates, flags) for Thunderbird's folder display. The actual emails live in the matching extension-less mbox file (e.g., INBOX) next to it. To export .eml files, use the ImportExportTools NG add-on in Thunderbird to export from that mbox mailbox.

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Also to EML: P7Z · OST · MSG

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Tested on macOS, Windows & Linux
Last verified Oct 2026

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Why convert MSF to EML?

Thunderbird stores each mail folder as two files: an extension-less mbox file containing all messages and an .msf index in Mork format used to speed up folder display. The .msf contains no email bodies or attachments - converting it to .eml would be like converting a card catalog to the books it references. The MSF is a disposable cache that Thunderbird rebuilds automatically if deleted.

How to convert MSF to EML

ImportExportTools NG FREE

Install ImportExportTools NG in Thunderbird, right-click the folder you want to export, and choose ImportExportTools NG > Export all messages in the folder > EML format. This reads the actual mbox mailbox file, not the .msf index.

About these formats

.MSF Mail Summary File (Mozilla Thunderbird / Mork index)

An MSF file is a Mail Summary File created by Mozilla Thunderbird (and SeaMonkey). It is a folder index - message headers, subjects, read/unread status - not the actual emails. You normally…

Open .MSF details →
.EML E-Mail Message (RFC 822 / MIME)

An EML file is one email message saved as a plain-text file - headers, body, and any attachments - in the internet-standard MIME/RFC 822 format. You do not need Microsoft Outlook to open…

Open .EML details →

Quality & what to watch

  • The .msf is a disposable cache; deleting it (with Thunderbird closed) causes Thunderbird to rebuild it automatically and never deletes any email.
  • The file that actually contains your emails is the same-named file with no extension (e.g., INBOX next to INBOX.msf) in standard mbox format.
  • You can also drag individual messages from Thunderbird onto your desktop - each drops as a separate .eml file without touching the .msf.

Frequently asked questions

I found a file called INBOX.msf - where are my actual emails?
In the file named INBOX (no extension) in the same folder. That is the mbox mailbox; the .msf is only its index.
Can any tool extract email content from an MSF file?
No. The .msf contains no email content. Work with the matching extension-less mbox file instead.
If I delete the MSF file, do I lose my emails?
No. The .msf is a cache that Thunderbird rebuilds on the next launch. Your emails are in the mbox file, which is unaffected.