OL98: (IMO) Winmail.dat Attachments Included in Received Messages

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Article ID: 193117 - View products that this article applies to.
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NOTE: These procedures only apply if you have installed Outlook with the Internet Mail Only option. To determine your installation type, click About Microsoft Outlook on the Help menu. If you have the Internet Mail Only option installed, you see "Internet Mail Only".

For information about the differences between Microsoft Outlook and Microsoft Outlook Express e-mail clients, click the following article number to view the article in the Microsoft Knowledge Base:
257824 OL2000: Differences Between Outlook and Outlook Express
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When you use Microsoft Outlook 98 to send e-mail 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.


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.


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.
If you would like to send RTF format to certain recipients and send others Plain Text, you have two options:
  • On the Format menu of the mail message, select Plain Text.
  • Select Plain Text on the General page of recipient's Contact form.


For more information on Winmail.dat attachments, please see the following articles in the Microsoft Knowledge Base:
149203 XFOR: Preventing Winmail.dat From Being Sent Over IMC

138053 XFOR: Preventing WINMAIL.DAT Sent to Internet Users


Article ID: 193117 - Last Review: October 26, 2013 - Revision: 2.0
Applies to
  • Microsoft Outlook 98 Standard Edition
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