Can Apple Mail open winmail.dat?

No. Apple Mail doesn't unpack Outlook's TNEF format, which is why it shows winmail.dat. Save it and drop it in the box above.

Do I need to install anything?

No. The opener runs in Safari, Chrome, Firefox or Edge. There is no app or extension to install.

No. The file is read in your browser on your Mac and is never sent to our server or stored.

Does it work on iPhone and iPad?

Yes. In the Mail app, save the winmail.dat to Files, then open this page in Safari, tap Choose files and pick it.

The attachments open in the wrong app. What now?

In Finder, right-click the file, choose Open With and pick the app you want, such as Preview or Pages.

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

How to open winmail.dat on a Mac

Why your Mac shows winmail.dat

Outlook can send messages in Microsoft's own Rich Text Format. When it does, it packs the formatting and all the attachments into one file using an encoding called TNEF. Outlook unpacks that file on the other end; Apple Mail doesn't, so you get winmail.dat instead.

Double-clicking it in Finder doesn't help. macOS asks which app to use, and none of the built-in ones (Preview, TextEdit, Pages) can read it. The file can also be named ATT00001.dat or have no useful name at all. It is the same thing, and the opener recognizes it by its contents.

Open winmail.dat on a Mac, step by step

Save the attachment. In Apple Mail, drag winmail.dat to your desktop, or right-click it and choose Save Attachment. It usually ends up in Downloads.
Drag the file from Finder onto the box at the top of this page. You can also click Choose files and pick it.
Read the message. You see the subject, sender, recipients, date and the text, with Outlook's rich text converted for display.
Download the attachments. Click the download button next to each file, or Download all (ZIP). Safari saves them to Downloads; a ZIP opens with a double-click in Finder.
Open the files as usual: PDFs and pictures in Preview, Word files in Pages or Word for Mac, spreadsheets in Numbers or Excel.

The same steps work in Chrome, Firefox and Edge on macOS.

Save the email as a PDF on your Mac

Click Save as PDF in the viewer. A clean print view opens with the header (subject, from, to, cc, date), the message and the list of attachment names, and the Print dialog appears.

In Safari, click the PDF button at the bottom-left of the Print dialog and choose Save as PDF. You can also use File > Export as PDF. In Chrome, set Destination to Save as PDF. The PDF is created by your own browser and opens in Preview.

Pictures attached to the email (JPEG, PNG, GIF) are printed after the list. Other attachments, such as Word files, are listed by name; download them separately.

Your email stays on your computer

The opener runs entirely in your browser on your Mac. The winmail.dat file is never uploaded to our server and never stored. Only this page and its scripts come from us; reading the file, unpacking the attachments and making the PDF all happen on your computer.

Limits

Pictures from the internet are blocked until you click Load remote images, because they can tell the sender you opened the email. They only appear in the PDF if you load them first.
Password-protected attachments stay protected. You still need the password.
Calendar invites come out as .ics files; double-click one to add it to Calendar.
Some very old or damaged files may not open.

Can you stop getting winmail.dat?

Not from your Mac. The sender has to change it in Outlook, by composing in HTML or Plain Text (File > Options > Mail in Outlook for Windows) or by making sure messages to you go out in Internet format. If one person sends these often, it's worth asking them.

More on the format on the winmail.dat opener page. Got an Outlook .msg file instead? See how to open .msg files on a Mac.