If you're having trouble opening a DAT file, I'll show you a simple and free way to do it. This method works on both Mac and PC. Just open your browser and go to winmaildat.com. It's a ...

If the DAT file is a video, you can open it with its associated video app. However, if you aren't sure what app it's intended for, VLC Media Player should be able to open it as well.

Q. I sometimes receive e-mail messages with a “winmail.dat” file attached that I cannot open. Why does this happen, and what can I do to fix it? A.

Right-click the DAT file on your PC and click "Open." Click "Select a program from a list of installed programs" and click "OK". Click "Microsoft Excel" from the list of programs on your computer.