I was confused by your answer regarding winmail.dat. The file cannot be opened traditionally, at least to obtain what the receiver believes to be valuable contents. Rather, it's used internally by ...

We keep getting e-mail attachments in winmail.dat files, and can't open them. What's going on? Is there a utility that can extract the attachments from these?

Problem: You can’t open files you receive from Windows users. Solution: Convert Winmail.dat files.

Many times when receiving mail attachments with the new Exchange-enabled Microsoft Entourage v.X from Windows users, you will get a winmail.dat file that is inaccessible under Mac OS X. Alan Sill ...

We just switched out SMTP Proxy from our Watchguard Firewall to our Meridius SPAM Filter and so far it is working a lot better. We are getting some complaints that winmail.dat files are being ...

I've got a few users that are now reporting that emails being sent out are showing up as winmail.dat attachments. This had been fine, and we switched over to Office 365 recently (in the last month ...

So instead of seeing the "rich text" formatting of the original message, you get a plain-text copy, plus a mysterious "winmail.dat" attached file.