When you use Microsoft Outlook to send e-mail containing attachments through the Internet, some recipients using e-mail clients, other than Outlook, report that the mail message includes an additional file called Winmail.dat. The file is usually very small, but cannot be opened in the mail message.

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The Winmail.dat file is used to preserve formatting that the sending client includes in the message, but is not recognized by the receiving client. In the case of Outlook, the Winmail.dat file includes Rich Text Formatting (RTF) instructions. This type of formatting is used with the Microsoft Outlook Rich Text Format and when using Microsoft Word as an e-mail editor.

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To avoid including Winmail.dat, use the Plain Text mail format. To select Plain Text for all messages, follow these steps:

1.	On the Tools menu, click Options and then Mail Format.
2.	In "Send in this message format", click to select Plain Text.

To send to certain recipients with RTF format and others with Plain Text, you must set the option for the recipient in either the Personal Address Book or the recipient's contact record.

To set Plain Text by recipient in the Address Book, follow these steps:

1.	On the Tools menu, click Address Book.
2.	In Show Names From, select the Personal Address Book.
3.	Select the addressee you want to set as Plain Text and on the File menu, click Properties.
4.	Click to clear the "Always send to this recipient in Microsoft Exchange Rich Text Format" check box and click OK.

To set Plain Text in the recipient's contact record, follow these steps:

1.	Open the recipient's record in the Contacts folder.
2.	Double-click the recipient's e-mail address.
3.	Click to clear the "Always send to this recipient in Microsoft Exchange Rich Text Format" check box and click OK.

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For additional information on Winmail.dat attachments, click the article numbers below to view the articles in the Microsoft Knowledge Base:

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