Thunderbird|Mozilla Mail Summary File magic bytes (.msf)
.msf file signature: 2F 2F 20 3C 21 2D 2D 20 3C 6D 64 62 3A 6D 6F 72 6B 3A 7A | application/octet-stream
Category: Email & PIM
The MSF (Mozilla Mail Summary File) is an index file used by Mozilla Thunderbird and earlier Mozilla Mail applications, maintained as part of the Mozilla mail storage system. It stores summary information for mail folders, including message headers, status flags, and folder metadata, allowing the client to load and navigate mailboxes more quickly. The format is a legacy support file and can usually be recreated if deleted; it does not normally contain active content, so risk is low.
Magic Bytes
Offset 0
2F 2F 20 3C 21 2D 2D 20 3C 6D 64 62 3A 6D 6F 72 6B 3A 7A
Sources: Gary Kessler
Validation Code
How to validate .msf files in Python
def is_msf(file_path: str) -> bool:
"""Check if file is a valid MSF by magic bytes."""
signature = bytes([0x2F, 0x2F, 0x20, 0x3C, 0x21, 0x2D, 0x2D, 0x20, 0x3C, 0x6D, 0x64, 0x62, 0x3A, 0x6D, 0x6F, 0x72, 0x6B, 0x3A, 0x7A])
with open(file_path, "rb") as f:
return f.read(19) == signatureHow to validate .msf files in Node.js
function isMSF(buffer: Buffer): boolean {
const signature = Buffer.from([0x2F, 0x2F, 0x20, 0x3C, 0x21, 0x2D, 0x2D, 0x20, 0x3C, 0x6D, 0x64, 0x62, 0x3A, 0x6D, 0x6F, 0x72, 0x6B, 0x3A, 0x7A]);
return buffer.subarray(0, 19).equals(signature);
}How to validate .msf files in Go
func IsMSF(data []byte) bool {
signature := []byte{0x2F, 0x2F, 0x20, 0x3C, 0x21, 0x2D, 0x2D, 0x20, 0x3C, 0x6D, 0x64, 0x62, 0x3A, 0x6D, 0x6F, 0x72, 0x6B, 0x3A, 0x7A}
if len(data) < 19 {
return false
}
return bytes.Equal(data[:19], signature)
}API Endpoint
/api/v1/msf
curl https://filesignature.org/api/v1/msf
See the full API documentation for all endpoints and parameters.
Related Formats
Frequently Asked Questions
What is a .msf file?
A .msf file is a Thunderbird|Mozilla Mail Summary File. The MSF (Mozilla Mail Summary File) is an index file used by Mozilla Thunderbird and earlier Mozilla Mail applications, maintained as part of the Mozilla mail storage system. It stores summary information for mail folders, including message headers, status flags, and folder metadata, allowing the client to load and navigate mailboxes more quickly. The format is a legacy support file and can usually be recreated if deleted; it does not normally contain active content, so risk is low.
What are the magic bytes for .msf files?
The magic bytes for Thunderbird|Mozilla Mail Summary File (.msf) files are 2F 2F 20 3C 21 2D 2D 20 3C 6D 64 62 3A 6D 6F 72 6B 3A 7A at byte offset 0. These bytes identify the file format more reliably than the extension alone.
How do I validate a .msf file?
To validate a .msf file, read the first bytes of the file and compare them against the known magic bytes (2F 2F 20 3C 21 2D 2D 20 3C 6D 64 62 3A 6D 6F 72 6B 3A 7A) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .msf files?
There is no officially registered MIME type for .msf files. Systems typically use application/octet-stream as a generic fallback when handling this format.
Is it safe to open .msf files?
Thunderbird|Mozilla Mail Summary File (.msf) files are generally safe to open. They are classified as low risk because they primarily contain data rather than executable code. However, always ensure files come from a trusted source.