Apple mail users get winmail.dat files as attachments

This happens when the email passes through a Microsoft Exchange server and you are set in the Outlook user’s contacts as someone who can receive messages in “Rich Text”. This saves the attachments as Microsoft TNEF stream files.

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 receive either a MIME attachment named "winmail.dat" or a MIME attachment with the type "application/ms-tnef."

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 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 file whether the user uses Outlook or not.

To resolve this issue ask the sender to remove the check box that says they can recieve Rich Text emails, or use TNEF's Enough utility to open the file. This is a freeware application that allows you to decode the attachment. click here to go to their website.