If your Outlook client is automatically attaching a winmail.dat file to your messages, stopping it from doing so is fairly easy. This issue arises when Outlook tries to send out emails in RTF format, as opposed to HTML or Plain Text format. Below you will find three ways of dealing with the issue, 1- stopping it all together, 2- stopping it for certain individuals, and 3- stopping it on a per message basis.

To prevent Outlook 2010 from attaching winmail.dat when you send any email

  1. Click the File tab >Options>Mail.
  2. Under Compose messages, in the Compose messages in this format list, make sure either “HTML” or “Plain Text” is selected:
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  4. Scroll down, and under Messages format, “When sending messages in Rich Text format to Internet recipients list, make sure to pick either “Convert to HTML format” or “Convert to Plain Text format” is selected:
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  6. Click OK.

Disable Sending RTF Message/Winmail.dat for all Messages Sent to Specific Recipients

  1. In the email box, double click the contact’s email address.
  2. Click “View more options for interacting with this person”:winmail3 
  3. Click Outlook Properties in the drop down list.
  4. In the Internet Format list, make sure either Let Outlook decide the best sending format or Send Plain Text only is selected:winmail4
  5. Click OK.

Disable Sending RTF Message/Winmail.dat on a Per Message Basis

  1. Compose a New Message.
  2. In the message window, on the Format Text tab, in the Format group, select Plain Text, and now you are ready.