Sudden change in attachments to win mail.dat from a Windows sender

Please read this old Apple Support document: If your email contains a winmail.dat attachment - Apple Support (Archived)

It may be a consequence of a recent system update, but the reasons for its appearance have not changed.

The following may also be of interest to you: "dat" files - Apple Community

Eugenio - I experienced the same thing. I never received Winmail.dat until recently, from mail senders I have been communicating with for months or years. To Apple: Installing a winmail.dat file reader is not a fix. it's a workaround, and I don't want a workaround.

I can only speculate as to the reason, and it may in fact be related to a software update. To inform Apple, use this link: Official Apple Support

Apple may or may not have anything useful to suggest. All I know is that winmail.dat attachments have never contained any information I found useful, so I have grown to ignore them. If someone expects me to read their email messages they can use conventional email protocols, not some creative version of it.

No, two replies does not make it “very common”. This problem is related to older clients on the sender side, and also possibly, their email providers:

If using Outlook solves it for you, you can download the Outlook app for macOS https://www.microsoft.com/en-us/microsoft-365/outlook/outlook-for-mac.

I believe the change is on the Sender's end.

In a Browser login to your WebMail & see if it is .dat file on the server.

The web will agree with any theory. Thank you for not posting links.

No, it's not just two replies. There are several articles across the web of people reporting the same issue, and similar in my case - suddenly without prompting, without having made any software changes.

I recently had the same problem and it is very troublesome. Have you received any information about the nature of the problem from the Apple?