Open winmail.dat files on Mac and Windows
A winmail.dat is neither a virus nor a broken file. Outlook packed the email's attachments into a TNEF container that only Outlook unpacks on its own. Mail Archive opens winmail.dat on Mac and Windows and lists the files inside, ready to open or save. Viewing is free and unlimited, even in the free edition.
Available on the Mac from version 1.3. The Windows version with these features is coming soon to the Microsoft Store.
Extract the attachments from winmail.dat
Save the file
Save the winmail.dat from your email app to your computer, for example to Downloads. If you saved the whole email as .eml or .msg, that works too.
Start Mail Archive
Get Mail Archive from the Mac App Store or the Microsoft Store and launch it. You don't need to add an email account to view files.
Open the file
Drag the winmail.dat into the window. Or click “Open file …” (or press Cmd+O / Ctrl+O), then “Choose file…”.
Open or save the attachments
Mail Archive lists the files inside. Click one to open it, or use the download icon and “Save as …” to store it wherever you like.
winmail.dat isn't registered with the operating system, because many other programs use the .dat extension too. Open it by drag and drop or with “Open file …”.
Why won't winmail.dat open?
Outlook can send messages in its own rich text format. When it does, it wraps formatting, attachments and some extra data into a file in TNEF (Transport Neutral Encapsulation Format). On the recipient's side, that file is almost always called winmail.dat.
Outlook reads TNEF itself and shows the attachments as usual. Many other email apps can't, or only partly. If you read your mail in Apple Mail, the iPhone Mail app or Thunderbird, you may see a single attachment called winmail.dat instead of the PDF or photo, often without a preview.
- The attachments aren't lost. They're all inside the winmail.dat.
- Renaming the file doesn't help. The container has to be unpacked.
- Whether TNEF is sent depends on the sender: on their message format in Outlook or on their mail server settings.
Archived emails are unpacked automatically
Attachments shown right away
When you archive your mailboxes with Mail Archive, winmail.dat attachments appear as individual files.
The original stays untouched
Mail Archive unpacks the container for display. The stored email with its original winmail.dat isn't changed.
Inside EML and MSG too
If a saved .eml or .msg file contains a winmail.dat, Mail Archive unpacks it when you open the file.
No upload, no cloud
Online winmail.dat converters only work if you upload the file to someone else's server. Yet attachments often contain contracts, invoices or ID scans.
Mail Archive unpacks the file on your computer. Nothing is uploaded, and the file never leaves your machine. Remote images in the email are only loaded when you explicitly allow it, so tracking pixels don't fire either.
Other options, honestly compared
| Option | Mac | Windows | Note |
|---|---|---|---|
| Mail Archive | ✓ | ✓ | Free viewing, no upload |
| Outlook for Windows | – | ✓ | Shows the attachments directly if Outlook is installed |
| Ask the sender to resend | ✓ | ✓ | HTML or plain text emails don't contain a winmail.dat |
| Online converter | ✓ | ✓ | The file is uploaded to a third-party server |
If one sender keeps sending winmail.dat, a quick tip helps: switch the message format in Outlook to HTML. In companies, the admin can turn off TNEF for external recipients on the mail server.
Questions about winmail.dat
Is a winmail.dat file dangerous?
The winmail.dat itself is just an Outlook container. What's inside can be harmful, just like any other attachment. Only open files from senders you trust.
How do I open winmail.dat on an iPhone?
Mail Archive is available for Mac and Windows, not for iPhone. Save the winmail.dat to the Files app or forward the email to yourself, then open it on your computer.
What does it cost?
Opening and viewing files is free and unlimited in the free edition. You can add up to 20 opened emails to your archive for free, or unlimited with Pro for a one-time €14.99, no subscription.
Do I have to upload the file?
No. Mail Archive works entirely on your computer. The winmail.dat and its attachments never leave it.
Why is there no message text after unpacking?
Depending on the sender, the text is either inside the winmail.dat or in the regular part of the email. If it's in the winmail.dat, Mail Archive shows it. Otherwise save the whole email as .eml or .msg and open that to see the text and the unpacked attachments together.
Can Mail Archive open EML and MSG files too?
Yes. See open EML files and open MSG files.
Mail Archive does more
Unpack winmail.dat the easy way
Download Mail Archive for free. Opening files is unlimited, even in the free edition.