Winmail.dat are e-mails that have been sent to you from someone who is using Outlook on the Dark Windows side. Not only have they sent it from out look by they have used rich text format. There is only one major problem with using Outlook in conjunction with Rich Text, you must use outlook to read the message as well. If you use any other program to read the message you will see this attachment in your e-mail. Some e-mail readers will let you see some off the text but not any of the formatting that is used some will display on the Winmail.dat attachment. There appear to be 2 fixes for this the first which comes form Macworld editor Christopher Breen. He says to send them the following e-mail replay:
“Dear User of Microsoft Outlook,
Thank you so much for taking the time to write. Regrettably, Iâ€™m unable to view the formatting you so carefully applied to your message because â€” and I know this may come as a shock â€” many, many people in the world do not use Microsoftâ€™s Outlook. Let me explain.
When you apply Outlookâ€™s Rich Text format to your email messages, only those recipients who open them in Outlook can see that formatting. The rest of us â€” and believe me, our numbers are significant â€” see the message along with a Winmail.dat attachment that we can not open. The problem can be compounded when any other attachment you included with the message is combined with this Winmail.dat attachment. So, for example, any pictures youâ€™ve sent of the familyâ€™s new iguana will go unseen.
To address this issue, please send future messages as plain text. (If you need help learning how to do this, see this Microsoft support document.) While Iâ€™m certain some of those you correspond with will miss the many fonts, underscores, shadow effects, and italic passages it is within your power to apply to your messages, Iâ€™m sure theyâ€™ll understand that you provide a greater service by sending messages that can be read by all recipients rather than just those whoâ€™ve adopted Microsoftâ€™s email client.
Thank you for your consideration.”
The second option is try to decode the Rich Text Winmail.dat attachment. Over at JoshJacob.com they have a program that can help in decoding these messages. The Program is called TNEF’s Enough. I have not tried this and can not attest to it. I did get the link form an update on the Christopher Breen MacWorld Post.