One of our customer reported that one of their recipient receives winmail.dat in the messages as the attachment. Based on analysis, we found that if the recipients of your messages receive an attachment called winmail.dat, you sent messages to them that included Microsoft Exchange Rich Text formatting (RTF), such as bold or italic text, but the recipients do not use an e-mail program that can read this format or does not support certain message formats or certain features that are included in the e-mail message.
To overcome this, try the following:
1) Using Outlook UI:
To select a message format do the following:
- On the Tools menu, click Options.
- On the Mail Format tab, under Message format, in the Compose in this message format list, click HTML or Plain Text.
2) Using Microsoft Fixit.
There is a fix available from Microsoft Fixit site regarding the same. Please refer the KB before you download it.
To fix this problem automatically, first install hotfix 957692 ( http://support.microsoft.com/kb/957692/ ) then click the Fix this problem link. Then click Run in the File Download dialog box, and follow the steps in this wizard.
Fix this problem
Microsoft Fix it 50041
Hope this helps.