It's 2012 and email is still an imperfect system - and the interoperability between Mac and PC is still inconsistent. We can put a Rover on Mars, but we can't make email seamless. I have a client who is on a PC and when she emails me attachments, I often (but not always which is even more maddening) receive them as the dreaded winmail.dat file.
What is a winmail.dat file, you ask?
The file is a rich text (or MAPI) message that is sent from Outlook to Exchange. When Exchange sends the message to an outside server it writes the MAPI message as a MIME attachment. The unfortunate side effect of this plan is that if the Outlook user has someone in their address book as a person who can receive "Rich Text" then the user will receive the TNEF (Transport Neutral Encapsulation Format) file whether the user uses Outlook or not.
The files are usually received by SMTP based e-mail programs from Microsoft Exchange and Microsoft Outlook users. The SMTP based e-mail program will usually either receive a MIME attachment named "winmail.dat" or a MIME attachment with the type "application/ms-tnef."
It was KILLING me. I'd have to ask her to resend. Or we tried using various file-sharing services. But it was a hassle for her.
Then, I found TNEF's Enough by Josh Jacob.
It is the sweetest little Mac program - it extracts the original attachment from the Microsoft TNEF stream that comes along with the win.dat attachment. Powerpoint files. Images. Word docs. Any attachment that she sends me and has been converted to a winmail.dat, TNEF Enough can open. Oh, and the explanation of a winmail.dat file is from his FAQ.
Below is a screenshot of TNEF's Enough. When I open the offending winmail.dat file in TNEF's Enough, it shows me the original email message as well as all the attachments. I can then choose one or more of them and "Export" from the menu.