eFax file format
application/octet-stream
Magic Bytes
Offset: 0
E3 10 00 01 00 00 00 00
The eFax file format (EFX) is a proprietary raster image format developed by J2 Global for digital facsimile transmissions. It serves as the native storage container for documents received via the eFax internet service and requires the eFax Messenger desktop application for viewing. Although classified as a legacy format superseded by PDF and TIFF standards, EFX files remain safe to open as they contain static document imagery without executable content.
Validation Code
How to validate .efx files in Python
Python
def is_efx(file_path: str) -> bool:
"""Check if file is a valid EFX by magic bytes."""
signature = bytes([0xE3, 0x10, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00])
with open(file_path, "rb") as f:
return f.read(8) == signatureHow to validate .efx files in Node.js
Node.js
function isEFX(buffer: Buffer): boolean {
const signature = Buffer.from([0xE3, 0x10, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00]);
return buffer.subarray(0, 8).equals(signature);
}
Go
func IsEFX(data []byte) bool {
signature := []byte{0xE3, 0x10, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00}
if len(data) < 8 {
return false
}
return bytes.Equal(data[:8], signature)
}API Endpoint
GET
/api/v1/efx
curl https://filesignature.org/api/v1/efx