MSF File

What are MSF files and how to open them

Are you having problems opening a MSF file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your MSF files.

What is a MSF file?

MSF files have multiple uses, and Mozilla Mail Summary is one of them. Read more about the other uses further down the page.

Mozilla Mail Summary File

Files that contain the .msf file extension normally hold an index of mail messages that have been created by a variety of different email applications.

The files do not contain the actual email contents sent or received by the user. Instead, they only contain an index of the emails with the mail headers and text summaries.

How to open MSF files

Important: Different programs may use files with the MSF file extension for different purposes, so unless you are sure which format your MSF file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different MSF openers which you will find listed below.

Last updated: August 4, 2026

All known file formats using extension .MSF

While Mozilla Mail Summary File is a popular type of MSF-file, we know of 2 different uses of the .MSF file extension. Different software may use files with the same extension for different types of data.

Amino/Nucleic Acid Multiple Sequence File

Amino/Nucleic Acid Multiple Sequence File (.MSF) is a plain-text alignment file that stores multiple biological sequences - either proteins (amino acids) or nucleic acids - already aligned for comparative analysis. Researchers use it when working with suites like GCG (Genetic Computer Group), or editors such as GeneDoc or UGENE, to view, edit or analyze sequence alignments. The file holds both metadata about the sequences (names, lengths, checksums, weights) and the alignment itself, so you can inspect variations, conserved regions, or evolutionary relationships.

When created, the file starts with optional comment or description lines, followed by a required header line beginning with "MSF:". That line declares the total alignment length, whether it's nucleotide or protein type, a date, and an internal checksum. Then it lists each sequence with its identifier (Name:), its length, its checksum, and its weight. After a line containing just "//", indicating the end of the name list, the aligned sequences appear in interleaved blocks: each block shows all sequence names followed by segments of their aligned sequence, with gaps represented by periods.

Internally, identifiers such as "!!NA MULTIPLE ALIGNMENT 1.0" (for nucleic acids) or "!!AA MULTIPLE ALIGNMENT 1.0" (for amino acids) may appear at the very beginning to mark the molecule type and version. The dividing header line that includes "MSF:" must end with two dots ("..") to separate header metadata from sequence listing. The sequence name part and its alignment portion are separated by whitespace. The checksum and weight values are numeric and represent internal consistency checks and relative importance or usage.

MSF opener for Windows

We have identified 2 MSF openers that are compatible with this specific type of MSF file.

Various apps that use files with this extension

These apps are known to open certain types of MSF files. Remember, different programs may use MSF files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about MSF file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.