It has happened to every computer user at some point or another. Someone sends you an email saying you should check out the attachment and when you try to open it the computer helpfully tells you that it doesn't know what that file type is and it can't open it.
This is exactly what can happen when you receive an email from someone using Microsoft Exchange. As you can see in the below quote, Exchange will store Rich Text Format information in their own specific format which people using programs other that the Windows versions of Mail or Outlook cannot read. Instead a Winmail.dat file is attached. This usually seems to happen when the attachment has been archived.
When an end user sends mail to the Internet from an Exchange Windows or Outlook client, a file attachment called Winmail.dat may be automatically added to the end of the message if the recipient's client cannot receive messages in Rich Text Format (RTF). The Winmail.dat file contains Exchange Server RTF information for the message, and may appear to the recipient as a binary file. It is not useful to non-Exchange Server recipients.
--source: Microsoft Support
The best thing that could happen would be to get whoever is sending you these mysterious Winmail.dat files to tell their Exchange server not to do that. But that would be impractical. So us Mac users must find another way: TNEF's Enough, a free application which you can just pop in your dock.
From here you can drag and drop that pesky Winmail.dat file onto the application and it will show you what's inside!Go Top