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MSF PST
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Convert MSF to PST

Can you convert MSF to PST?
Verified by Adam B.· reviewed by FE Editorial ·updated Jul 14, 2026
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Is it possible to convert MSF to PST?
No - not a direct conversion.

The .msf index has no email bodies or attachments - the extension-less mbox file beside it contains the actual messages. To move Thunderbird mail into Outlook, export from the mbox file (not the .msf) using ImportExportTools NG, then import the resulting .eml files into Outlook.

No direct path
Also to PST: OST · SBD · NSF

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Tested on macOS, Windows & Linux
Last verified Oct 2026

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Why convert MSF to PST?

Thunderbird keeps each folder as two files: an extension-less mbox file with all messages and an .msf Mork-format index used for fast folder display. A .pst is Outlook's proprietary content store for complete emails, contacts, and calendar items. The .msf holds none of that content, making any conversion meaningless.

How to convert MSF to PST

ImportExportTools NG FREE

Install ImportExportTools NG in Thunderbird and export the folder as .eml files, then import those into Outlook via File > Open & Export > Import/Export. Work from the mbox mailbox file - the .msf plays no role in migration.

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 →
.PST Outlook Personal Storage Table

A PST file is a Microsoft Outlook database that stores an entire mailbox in one file - emails, contacts, calendar appointments, tasks, and notes. The standard way to open it is Microsoft…

Open .PST details →

Quality & what to watch

  • MSF files are disposable caches; Thunderbird rebuilds them automatically. The mbox file (no extension) is what holds the email content.
  • Tools that claim to convert .msf to .pst are either reading the matching mbox file (not the .msf itself) or producing empty output.
  • MSF files can be safely skipped when migrating a Thunderbird profile - copy only the extension-less mailbox files.

Frequently asked questions

Does INBOX.msf contain my emails?
No. The emails are in the file named INBOX (no extension) in the same directory. The .msf is only an index.
A converter says it can open MSF files and export to PST - is that accurate?
Only if it is actually reading the matching mbox file, not the .msf. A tool reading only the .msf will produce empty or header-only output.
Is it safe to skip MSF files when copying a Thunderbird profile?
Yes. Copy the extension-less mailbox files; Thunderbird regenerates the .msf indexes on first launch.