NEW: macOS High Sierra compatible

What is WinDat Opener?

WinDat Opener is a program for Mac OS X that extracts attachments from TNEF (winmail.dat) format files. It's the most popular and highest rated TNEF decoder on the app store.


Windat Opener is also available for the iPhone and iPad; for more information, see here.

Why WinDat Opener?

WinDat Opener is the easiest way to deal with those pesky winmail.dat files you keep on getting as attachments sent from Windows machines. But WinDat Opener is also powerful:
  • Works with any email client. Just drag-and-drop winmail.dat files from anywhere - WinDat Opener does the rest
  • New in version 2.1: Decodes embedded Windows Mail notes
  • New in version 2.1: Windows "code page" support. WinDat Opener now decodes winmail.dat files that use Windows "code page" encoding for non ASCII character sets. Now data in encoding including Korean, Thai, Chinese, Arabic, Turkish, etc are all decoded
  • New in version 2: Decode contact (vCard) and appointment (iCal) information embedded in individual data fields within winmail.dat files rather than attached as files (see the FAQs for more information)
  • Decodes all TNEF format (winmail.dat) files
  • Highest rated and most popular decoder on the App Store
  • Simple drag-and-drop operation
  • Unlike other TNEF decoders, WinDat Opener preserves attachment dates, making it easy to keep track of file versions
  • Allows files to be opened from within WinDat Opener, allowing the contents to be examined without copying the attachment to a new location

What are TNEF files?

Microsoft e-mail programs written for Windows, such as Outlook, sometimes send e-mails in the Transport Neutral Encapsulation Format (TNEF). Most other e-mail programs, including Apple Mail and Microsoft Entourage, do not understand TNEF. If your e-mail program doesn't understand TNEF, instead of seeing the e-mail and/or attachment, you may only see an attachment named "winmail.dat" or "Part 1.2" that you cannot open. Also, sometimes you may receive a TNEF attachment with a generic name such as ATT00008.dat or ATT00005.eml instead. While almost all attachments named "winmail.dat" are TNEF, you could receive non-TNEF attachments with names ending ".dat" or ".eml", or which are named or labeled "Part 1.2".

WinDat Opener for the iPhone and iPad

Looking for a iPhone and iPad version of WinDat Opener? WinDat Opener lives here: WinDat Opener for iOS

System Requirements

OS X 10.6.6 (Snow Leopard) or later

Recent Announcements

  • WinDat Opener is OS X Mavericks compatible WinDat Opener is the most popular and best rated app on the Apple App store for decoding winmail.dat files, including files with embedded appointments and embedded contact information. And ...
    Posted Oct 6, 2013, 5:16 AM by Sandy McGuffog
  • WinDat Opener V2 is available Version of 2 of WinDat Opener for iOS is now available on the App Store. Already the most popular and highly rated winmail.dat file (aka TNEF file) decoder on ...
    Posted Aug 26, 2011, 7:37 AM by Sandy McGuffog
  • The Mac App store is live The Mac App store is live, and WinDat Opener is available!
    Posted Jan 7, 2011, 4:35 AM by Sandy McGuffog
  • WinDat Opener for OS X to become available on January 6 Apple announced on Thursday that its Mac App Store will open in three weeks, on Thursday, January 6. The Mac App Store is designed to offer Mac OS X users ...
    Posted Dec 18, 2010, 12:52 AM by Sandy McGuffog
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