Microsoft Outlook Offline Storage Folder File (.ost)
.ost file signature | application/vnd.ms-outlook-pst
Microsoft Outlook Offline Storage Folder File
Magic Bytes
Offset 0
21 42 44 4E 2E 2E 2E 2E 53 4D
Sources: Apache Tika
All Known Signatures
2 signature variants are documented for .ost files across multiple sources.
| Hex Signature | Offset | Sources |
|---|---|---|
| 21 42 44 4E 2E 2E 2E 2E 53 4D | 0 | Apache Tika |
| 21 42 44 4E | 0 | Gary Kessler |
Extension
.ost
MIME Type
application/vnd.ms-outlook-pst
Byte Offset
0
Risk Level
Safe
Validation Code
How to validate .ost files in 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
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);
}How to validate .ost files in 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
/api/v1/ost
curl https://filesignature.org/api/v1/ost
See the full API documentation for all endpoints and parameters.
Frequently Asked Questions
What is a .ost file?
A .ost file is a Microsoft Outlook Offline Storage Folder File file. Microsoft Outlook Offline Storage Folder File
What are the magic bytes for .ost files?
The magic bytes for Microsoft Outlook Offline Storage Folder File files are 21 42 44 4E 2E 2E 2E 2E 53 4D at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.
How do I validate a .ost file?
To validate a .ost file, read the first bytes of the file and compare them against the known magic bytes (21 42 44 4E 2E 2E 2E 2E 53 4D) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .ost files?
The primary MIME type for .ost files is application/vnd.ms-outlook-pst.
Is it safe to open .ost files?
Microsoft Outlook Offline Storage Folder File (.ost) 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.