View the content of winmail.dat file on your IOS Devices. Winmail App is the Best Winmail.dat Viewer for IOS 8 Devices Supports iPhone 6, iPhone 6 Plus, iPad 3, iPad Air, iPhone 5, iPhone 5S. P.S. - No need to explicitly open the application. Application register itself to work with your email client on iOS device. - Install Winmail App on your iOS device. - Open your mail containing Winmail attachment. - Tap the winmail.dat file - You're instantly presented with a list of Winmail file contents.