Guide · Decode
How to open a winmail.dat file
You were expecting a document, a photo, or a spreadsheet — and instead the email arrived with a single mystery attachment named winmail.dat that nothing on your computer will open. It is not corrupt and it is not spam. It is a TNEF wrapper that Outlook packed your real files into. MSGView decodes that wrapper right in your browser and hands back the actual attachments, with no Outlook and nothing uploaded.
Open winmail.dat in 3 steps
- Open MSGViewGo to msgview.app in any modern browser on Windows, Mac, Linux, ChromeOS, iOS, or Android. There's nothing to install and no account to create.
- Drop your winmail.dat fileDrag the winmail.dat onto the page. It's read into your browser tab and decoded there — the file is never sent to a server, which you can confirm in your browser's Network panel.
- Save the real attachmentsMSGView unpacks the TNEF wrapper and lists the genuine files inside. Save them one by one, or grab everything at once as a .zip.
What is winmail.dat, and why did you get one?
A winmail.dat file is Outlook's TNEF attachment — short for Transport Neutral Encapsulation Format. When someone sends a message from Outlook using Rich Text Format (RTF), Outlook bundles the message's formatting and its real attachments into a single binary file and names it winmail.dat. Outlook on the receiving end knows how to unpack it, so the recipient never notices. But Gmail, Apple Mail, Thunderbird, and most other mail apps don't understand TNEF, so they simply show you the raw wrapper — and the files you actually wanted stay locked inside.
The fix isn't on your end: the sender picked RTF (often without realizing it). Until they switch to plain text or HTML, you'll keep receiving winmail.dat wrappers. MSGView decodes them so you can get to your files today, whatever the sender does next. It reads the TNEF stream, extracts each embedded attachment with its original filename, and even handles CJK, Cyrillic, and other encodings so international filenames and text come through intact.
Private by design
Free online winmail.dat decoders usually make you upload the file to a stranger's server — a bad idea when the wrapper contains contracts, invoices, or personal documents. MSGView never does that. All decoding happens inside your browser tab; the file's bytes never leave your device, and there's no sign-up, no watermark, and no size trap. You can handle winmail.dat files up to 100 MB, and open the Network panel to verify for yourself that nothing is transmitted.
FAQ
What is a winmail.dat file?
It's a TNEF (Transport Neutral Encapsulation Format) attachment created by Outlook. It packs rich formatting plus the email's real attachments into one binary file. Non-Outlook mail apps can't read it directly, so they display the raw winmail.dat instead of the files inside.
Why did I receive a winmail.dat instead of my actual attachment?
The sender's Outlook sent the message in Rich Text Format. RTF makes Outlook wrap the real attachments in a TNEF winmail.dat file. Any mail client that doesn't understand TNEF — Gmail, Apple Mail, and most others — shows you the wrapper rather than the contents.
Can I open winmail.dat on a phone or a Mac?
Yes. MSGView runs entirely in the browser, so it decodes winmail.dat on iOS, Android, Mac, Windows, Linux, and ChromeOS with nothing to install. Just open msgview.app and drop the file in.