OST
application/vnd.ms-outlook-pst
Magic Bytes
Offset: 0
21 42 44 4E 2E 2E 2E 2E 53 4D
Offline Storage Table (OST) is a proprietary database file format developed by Microsoft for storing synchronized copies of mailbox data. It allows users of Microsoft Outlook to access email, calendar items, and contacts while disconnected from the Exchange server. While the format itself is considered safe, OST files are strictly tied to specific mail profiles and are not intended for manual transfer or migration between different computer systems.
Validation Code
How to validate .ost files in Python
Python
def is_ost(file_path: str) -> bool:
"""Check if file is a valid OST by magic bytes."""
signature = bytes([0x21, 0x42, 0x44, 0x4E, 0x2E, 0x2E, 0x2E, 0x2E, 0x53, 0x4D])
with open(file_path, "rb") as f:
return f.read(10) == signatureHow to validate .ost files in Node.js
Node.js
function isOST(buffer: Buffer): boolean {
const signature = Buffer.from([0x21, 0x42, 0x44, 0x4E, 0x2E, 0x2E, 0x2E, 0x2E, 0x53, 0x4D]);
return buffer.subarray(0, 10).equals(signature);
}
Go
func IsOST(data []byte) bool {
signature := []byte{0x21, 0x42, 0x44, 0x4E, 0x2E, 0x2E, 0x2E, 0x2E, 0x53, 0x4D}
if len(data) < 10 {
return false
}
return bytes.Equal(data[:10], signature)
}API Endpoint
GET
/api/v1/ost
curl https://filesignature.org/api/v1/ost