How to Open Winmail.dat Files


Cary, NC – Small businesses and entrepreneurs don’t usually have IT departments. So what do you do when you get a proprietary format file as an email attachment like Winmail.dat?


Winmail.dat is a compression format of Microsoft Outlook or MS Exchange Server. If you’re using Gmail or MacMail or some other email client, you may have trouble opening a Winmail.dat file.

Technically, the file format is usually a TNEF, or Transport Neutral Encapsulation Format. Only Microsoft broadly supports this protocol. Messages are encoded with TNEF automatically from Outlook and Exchange.

How to Open Winmail.dat Files

It’s embarrassing to have to ask a client or prospect to resend the file in another format. Fortunately, there are some apps that can help you open a Winmail.dat file even if you don’t use Microsoft Outlook.

  • – This is a website where you can upload the file to be decompressed into its component parts. Just today, a client sent me a Winmail.dat attachment and I was able to decompress it into the original PDF in about 10 seconds. The service is free.
  • iOS Decoder – This little app works on the iPhone and iPad. If you read your email on a mobile device or tablet, this is a handy way to go.
  • Winmail Reader – This app is for users on Windows computers who don’t have Outlook. It installs on your computer.

More Winmail.dat converters are listed on the Mozilla website.


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