How to open a winmail.dat file

Winmail.dat files (also know as TNEF attachments) are special email attachment files sent by Microsoft servers. This article explains shortly how to open a winmail.dat file sent by email to you.

How to decode a winmail.dat file online

Hopefully, you don’t need to install any application to convert a winmail.dat file. You can do it online directly from your browser. Just follow the below steps:

Time needed: 1 minute.

Opening a winmail.dat file online

  1. Save the winmail.dat attachment to your device

    For most of the e-mail clients, you just need to click/tap on the winmail.dat attachment file and select “Save attachment”. If you have difficulties or don’t file this option, check how to save an attachment on web email clients, iPhone and iPad, or Outlook.

  2. Open the Winmail.dat Reader website

    In your web browser, type www.winmail-dat.com in the address bar and press Enter (or simply click on the link)

  3. Open the winmail.dat file

    Click on “Choose file” and select the file that you just saved on step 1

  4. Decode the winmail.dat file

    Press the Decode button to decode the winmail.dat file.

Interpreting the results

A winmail.dat file (or TNEF Attachment) includes not only the e-mail attachments, but it may also contain other email contents like subject and body. When decoding a file through the online Winmail.dat Reader you will see the results in two blocks:

Example of TNEF file opened by the Winmail.dat Reader
Example of parsed TNEF attachment

The Message block contains the important information the decoder parsed from the winmail.dat attachment, which might include the email subject and message body.

The Attachments block contains a list of all attachments successfully read from the file. You can download the decoded attachment by clicking/tapping on it. Sometimes the parser might not be able to decode one or another attachment. In this case, you see a “(empty)” in the place of the attachment size.

How to open a winmail.dat file

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