Messages sent from older versions of Microsoft email apps, like Outlook or Microsoft Exchange, might include an attachment with winmail.dat in the name. The file doesn't appear in the sending app, but it does appear in Mail. In other email apps, it might appear as a MIME section named application/ms-tnef. This happens when the sending app uses Transport Neutral Encapsulation Format (TNEF).
The winmail.dat file might not contain any useful information or it might contain a document or other file.
To open a winmail.dat file on your iPhone, iPad, iPod touch, or Mac, follow these steps:
- Open the message in Mail.
- Touch and hold the winmail.dat attachment. Or on a Mac, choose File > Save Attachments to save the winmail.dat file.
- Open the file with a third-party winmail.dat viewer. You can find these types of viewers on the App Store.