Just open your browser and go to winmaildat.com. It's a straightforward website that lets you upload and open DAT files without needing to sign up or provide an email.

If the DAT file you're trying to open is text, you can convert the file into text in the Microsoft Excel program by first saving it as a CSV file.

If you can’t convince the sender to use standard email formats, you also have a few options for reading these Winmail.dat-formatted messages. On the Mac, TNEF’s Enough, can open winmail.dat files.

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 ...