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 straightforward ...

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. The winmail.dat file usually appears because various ...

.dat can mean many things. data of any type quite often ends up with these extensions. How about using the app that created them? You can also try viewing them in notepad.