Jodi writes in:

I wasn’t sure who I should contact about this, so i am sending this to you. As of late, word attachments coming from my friend on a Windows XP Machine appear as “winmail.dat” files.
When I try to open these, the text runs about 150pp long, (it’s a 4page doc) and the text looks like this:
?<‡META †[1]0 ?Xt=”‡$.
It shows garbage like that over and over again. Admin Can you help me open them? If I forward the message on to a windows user it is fine! What gives?
Jodi have been dealing with this one for a while and there seems to be no rhyme or reason as to when they appear and when they don’t appear. We investigated the possibility of drag and drop causing it – but that wasn’t it consistently. But we found a utility called TNEF’s Enough for our Mac friends here:
You can simply drag winmail.dat into this application and BAM! There is your data ma’am, can we do anything else for you today?
UPDATE: Fix this on your exchange 2007 server by doing this:

On the exchange server, go to global settings, Internet Message Formats, Default Properties, Advanced tab, for “Exchange Rich-Text Format” select “Never Use”.

This will prevent your Exchangeserver from using Rich-Text Format and creating winmail.dat files.

From TNEF’s website:

TNEF’s Enough allows Macs to read and extract files from 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.

TNEF’s Enough is a freeware application