Whether you have a Mac or a PC you will find that some files can’t be read as they are scripted for a particular computer. One format that you may receive in an attachment is a winmail.dat file. If you find your Mac doesn’t allow you to open it then the follow instructions will help you.
First you will need to download the free application call TNEF’s enough which you can find on Josh Jacob’s website. You need to download and install it into your applications folder. Once you have done that you need to run the application by double-clicking on it. Drag the email attachment out of the email and drop it on top of the TNEF’s enough icon in the dock. Double click the file in the bottom half of the window that appears. The TNEF’s enough app will then ask you where you would like to save the new file, which is where convenient for your own access. Then you can go to that location you have saved it to and open the file.
Winmail.dat file is usually a Windows file that has been sent using Outlook.