- Kelly's World- A View into the mind of Uber Geek, Kelly Adams - http://www.kgadams.net -

What the heck is a winmail.dat attachment?

Being new to the Macintosh, I’m “discovering” things for the first time that are ancient history for most Mac users. That is entirely to be expected. But I must admit I totally mis-diagnosed a mysterious email attachment I received today.

At the bottom of the email was this enigmatic information:

The file was from my brother, and I was actually expecting something from him- some photos. I immediately went looking to find out what “Corel Snapfire Plus [1]” is, discovered that it is a Windows-only application, and thought I had my solution. Obviously, thought I, winmail.dat files are some sort of proprietary image format produced by Snapfire.

I was completely wrong. Apparently, winmail.dat files [2] are the result of using Rich Text and attachments with Windows Outlook to send email to non-Windows users. The file itself is encoded using something called “Transport Neutral Encapsulation format”- the link above explains this proprietary Microsoft format in a bit more detail. Apparently, this affliction only impacts mail sent with Outlook (the exchange client): not Outlook Express, or Windows Mail (the POP/SMTP mail clients).

There are a couple of ways of decoding winmail.dat files on the Mac: the two main choices are:

I bought OMiC, so hopefully that’s the last time that particular problem will surprise me 🙂