Free local winmail.dat (TNEF) extractor
Unpack winmail.dat
attachments locally.
Open Outlook winmail.dat (TNEF) attachments right in your browser and save the enclosed files without uploading private emails.
Drop your winmail.dat file here.
Or choose a winmail.dat (or ATT00001.dat) file from your device, up to 50 MB. No account. No uploads.
Up to 50 MB and 128 attachments. Unpacked locally in memory on your device.
Use is subject to our terms. Read the privacy policy.
Why did I receive a winmail.dat file?
When someone using Microsoft Outlook or Exchange sends an email formatted as Outlook Rich Text, Outlook wraps the formatting instructions and any attached documents inside a single TNEF (Transport Neutral Encapsulation Format) container named winmail.dat (or ATT00001.dat).
Email clients outside Windows Outlook—including Apple Mail on Mac, iPhone and iPad, Gmail and Thunderbird—do not unpack TNEF streams automatically, leaving the real PDF, spreadsheet or photo hidden inside winmail.dat.
Unpack attachments without uploading private mail
Email attachments often contain invoices, contracts or personal documents that should not be uploaded to a third-party conversion server. This tool verifies the TNEF signature (78 9F 3E 22), validates attribute checksums, and extracts the enclosed files in memory inside your browser.
If your .dat file came from another program rather than an Outlook email, read what a .dat file is and how to open it or drop it into the file type checker. For native Outlook .msg to .eml conversion on macOS, explore the File Sniff app.
Common questions
Are my email attachments uploaded anywhere?
No. Your browser reads the winmail.dat package locally in memory and extracts the enclosed files directly on your device. Nothing is sent to a server. See our privacy overview.
Why did it say my .dat file is not a valid winmail.dat package?
Only Microsoft Outlook TNEF files (starting with the signature 78 9F 3E 22) use the winmail.dat format. Many other programs use .dat for ordinary PDFs, images or app data. Check the file with the file type checker or read what a .dat file is and how to open it.
What if my Outlook file ends in .msg instead of winmail.dat?
Outlook .msg files use Microsoft’s OLE2 Compound File format rather than TNEF. Open them locally in your browser with the Outlook .msg & .eml viewer.