I'm having this problem, when opening a word document, combining it into email (with Outlook) and checking the "attach file" box. The file is received with .dat extension. It's the same word document, you just have to change the .dat back to .doc. Anyway this is very annoying and besides, how do you explain that to every recipient...

How are you "Combining" it with Outlook?

"It's the same word document, you just have to change the .dat back to .doc." Are yopu that it is not changing the attachment to Winmail.dat? If so then there is much about that having to do with Microsoft Exchange Client or: "TNEF (Transport-Neutral Encapsulation Format) is important as far as attachments go. TNEF is a proprietary method for encoding RTF messages that are sent across the Internet. A TNEF-encoded message contains a plain text version of the message and an attachment that contains the RFT version or the Rich Text Format — any objects such as pictures or other attachments that were sent with a message. When a message containing TNEF information is received by a mail client that does not understand what TNEF is, an attachment is created with the name Winmail.dat. In some cases, the mail server looks for and strips out the TNEF information and the Winmail.dat information." from "How to Troubleshoot Sending and Receiving Internet E-Mail with Outlook" a Microsoft Support WebCast transcript. In either case the problem is not with what you are sending it is a problem with how they are receiving it or their ability to do so. HTH Bryan