What is Thunderbird Application and all The Related Info Mentioned Here!


Thunderbird is the popular email client which is available for all major platforms. It is an open source client which has MBOX as the main file format to which emails and other mailbox functionality data resides.

Along with MBOX, Thunderbird also has MSF and SBD file formats which serve different function for the email client.

What is MSF file?

MSF file is Mail Summary File which contains email headers and other information except body or content of an email.

MSF files are also associated with EarthLink E-mail Message File (EarthLink Inc.), Multiple Sequence File, Netscape Mail Summary File (Netscape) and SeaMonkey along with Mozilla Thunderbird. The latest addition in this list is the Eudora 8 version.

Thunderbird creates two types of files in the user profile directory which are as follows:

  • Without Extension: This type of file with no extension is called MBOX file which stores all the information of the mailbox in Thunderbird.
  • With Extension: This type of file is associated with .msf extension which contains the summary of the email and not the actual message. It is stored in the user profile in Thunderbird.

How to Locate MSF file in Thunderbird?

MSF file location in Thunderbird can be checked from the below steps:

  • Launch the Thunderbird application on your system.
  • Go to Tools > Account Settings > Server Settings.
  • Now check the Local directory row of the settings and copy it.
  • open msf files in thunderbird
  • Paste the copied local directory in the file explorer, where the entire file directory of Thunderbird can be seen along with MSF files.
  • locate msf files

How to open MSF files?

There are some situations in which the user receive attachment in email containing MSF files and most of the times not able to open them due to unfamiliarity of the file format.

Opening MSF Files - In Windows if the user double click the MSF file extension, then Windows ask to “Open with” response and if a dedicated application is already installed then only the MSF file can be opened otherwise not.

MSF files can be opened in the Windows if the user has Thunderbird email client or Netscape web browser.


This will help the user in locating MSF files on the system and opening MSF using Thunderbird application. If you also want to open mailbox files in Thunderbird, you can use the free ImportExportTools add-on for this task. However, if email migration to other email client is involved, then go for a professional Thunderbird to Outlook Converter.