What is MSF File Extension?


MSF stands for Mail Summary File which is a file format of Thunderbird email client. It holds the summary and headers of emails. Thunderbird email client saves emails in MBOX and MSF file formats. The MBOX holds the entire components of emails whereas MSF retains the index of that particular mail. The MSF file format aims that other apps import emails from the MBOX without using other third apps.


It falls in email related data files category.

Supportive Apps

It is supported by Mozilla Thunderbird only.


The developer is Mozilla.


The signature is in hexadecimal form- 2F 2F 20 3C 21 2D 2D 20 3C 6D 64 62 3A 6D 6F 72 6B


The location of the file format is depended on the Windows version you are using.

Windows Vista/7/8/8.1

C:\Users\Username\AppData\Roaming\Thunderbird\Profiles\ xxxxx.default

Windows XP/Windows Server 2003

C:\Windows\Application Data\Mozilla Thunderbird\Profiles\xxxxx.default

How to View MSF File Extension

The file format is accessed by Mozilla Thunderbird email client.