Winmail Opener: How to read TNEF-encoded email messages

Microsoft Outlook and Exchange Server often store and transport messages in TNEF, a proprietary format Microsoft uses to encapsulate email messages. A non-Microsoft email client that doesn't know how to interpret TNEF will simply display the message as a plaintext email with WINMAIL.DAT listed as an attachment -- which means that any attached data will be unreadable. One way around this issue is to use a program like Winmail Opener, a free utility that decodes and reads TNEF.

Not long ago, I covered TNEF View, a utility for reading email messages encoded in Transport Neutral Encapsulation

Format, the proprietary format Microsoft uses to encapsulate messages. Microsoft Outlook and Exchange Server often store and transport messages in TNEF format.

To non-Microsoft mail readers, a TNEF email looks like a plaintext copy of the message with an attachment named WINMAIL.DAT. The attachment contains a richly formatted version of the message, any OLE-embedded objects, any Outlook-specific features (such as custom forms), and attached files or messages.

An email client that doesn't know how to interpret TNEF will simply display such a message as a plaintext email with WINMAIL.DAT listed as an attachment -- which means that any attached data will be unreadable.

One way to get around this issue is to use an external program that reads TNEF. I've recently encountered a free application called Winmail Opener that handles the vast majority of the work needed to decode and understand TNEF.

Winmail Opener runs a few different ways:

  • As a window into which you can drag-and-drop TNEF-encoded files
  • As a command line, which you can use to do batch decodes of many files
  • As a right-click context menu item, which can be used to open TNEF files from Explorer or associated with .DAT files

When you first launch the program, it gives you a wizard-style interface for opening messages. When a message is dragged and dropped onto the program, its text and any assorted attachments are listed and can be extracted and saved.

When run as a command line, it takes up to two parameters -- a source file and a target directory -- and can be used in conjunction with a batch file to automatically process all messages in a given directory.

About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.

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Related information from SearchExchange.com:

  • Tip: Decipher a WINMAIL.DAT package without using Microsoft Outlook
  • Our SearchExchange.com experts' favorite freeware
  • The Microsoft Outlook Toolbox
  • Reference Center: Outlook and Exchange administration tools

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  • This was first published in July 2006

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