Is winmail.dat a virus?

Not by itself. It is a normal container made by Outlook. But like any attachment, the files inside can be anything, so only open documents from people you trust.

Why did I get winmail.dat instead of the attachments?

The sender used Outlook with Rich Text Format, and your mail program can't read that format. The attachments are packed inside the winmail.dat file. Drop it in the box above to get them out.

What about ATT00001.dat or a file called noname?

These are usually the same thing under a different name. The opener checks the contents, so drop them in just like winmail.dat.

Yes. There is no signup and no cap on the number of files: very large batches are limited only by your device's memory.

Are my files uploaded?

No. Everything runs in your browser. Your file is never sent to our server or stored.

Does it work on a phone?

Yes, in mobile browsers on iPhone, iPad and Android. Save the attachment to Files or Downloads first, then choose it here.

Can I save the message as a PDF?

Yes. Click Save as PDF and choose Save as PDF in your browser's print dialog. Attachments other than pictures are listed by name and downloaded separately.

Winmail.dat opener: free online viewer

What is a winmail.dat file?

Winmail.dat is a container that Microsoft Outlook creates when it sends a message in its own Rich Text Format. Outlook packs the formatting and every attachment into one file using an encoding called TNEF (the file type is application/ms-tnef).

Outlook on the other side unpacks it without you noticing. Most other mail programs don't understand TNEF, so Apple Mail, Thunderbird, some Gmail setups and many phone mail apps show you a single attachment you can't open. The real attachments are inside it.

The file isn't always called winmail.dat. You may see ATT00001.dat, Part 1.2, noname or a name ending in .tnef. The opener looks at what is inside the file, not at its name, so any of these work.

How to open winmail.dat, step by step

Save the attachment from your email to your computer (usually it lands in Downloads).
Drag the file onto the box at the top of this page, or click Choose files and pick it. You can add several winmail.dat files at once.
Read the message. The viewer shows the subject, sender, recipients, date and the text. Outlook rich text (RTF) bodies are converted so you can read them.
Get the attachments. Each file found inside is listed with its name and size. Click the download button next to a file, or Download all (ZIP) to get them together.
Open attached emails if there are any. An email forwarded as an attachment inside the winmail.dat opens in the same viewer.

Want a copy of the message on paper or as a file? Click Save as PDF. A print-ready view opens and your browser's print dialog appears; pick Save as PDF as the destination.

Your email stays on your computer

The opener runs entirely in your browser. Your winmail.dat file is read on your own computer and is never uploaded to our server or stored anywhere. Only this page and its scripts come from us; the unpacking, the display and the PDF all happen on your device.

That matters, because a winmail.dat often carries contracts, invoices or personal photos. You don't have to send them to a stranger's server to read them.

What you'll see

The message text, with its formatting where possible. HTML emails are shown as they were designed, in a locked-down frame where no scripts run.
Pictures from the internet are blocked at first, because they can tell the sender you opened the email. Click Load remote images if you trust the message. Pictures embedded in the email show normally.
Every attachment: Word and Excel files, PDFs, pictures, and anything else the sender attached.

Limits

Password-protected documents stay protected. The opener gets the file out, but you still need the password to open it.
Calendar invites appear as an .ics attachment you can download and open in your calendar app.
Some very old or damaged files may not open. If the file was cut off in transit, ask the sender to send it again.
Fonts follow your browser, so the message may look slightly different from the sender's screen.

How the sender can stop sending winmail.dat

The fix is on the sender's side. In Outlook for Windows they can go to File > Options > Mail and set Compose messages in this format to HTML or Plain Text. If a contact still gets winmail.dat, the sender can check that contact's settings and make sure messages to them go out in Internet format rather than Rich Text.

Until then, this opener gets you the files. On a Mac? See how to open winmail.dat on a Mac. Got a normal email saved as a file instead? Try EML to PDF or MSG to PDF.

Winmail.dat opener

Open your winmail.dat file