
Even if your system is capable of displaying the file, it does not contain any useful information. Because this file is in a Microsoft proprietary Outlook/Exchange format, you may not have an application installed that can decode this file and display it. If you try to open winmail.dat, you will probably be prompted to specify the application that should be used to open the file. Because of this, any attachments sent with the original message are not displayed in Thunderbird's message pane.

The file is not recognized by other email clients. This file contains formatting information for messages that use Microsoft's proprietary TNEF standard and any attachments sent with the original message.

When people send messages from incorrectly configured Microsoft Outlook email clients, a file attachment called winmail.dat may be added as an attachment to the message.
