Winmail.dat attachments
When using Microsoft Outlook to send messages with Rich Text Formatting, the recipient receives an attachment called Winmail.dat which cannot be opened. The Winmail.dat attachment includes formatting instructions specific to Rich Text Formatting. To resolve this problem, change the default format in Outlook from Rich Text Formatting to either Plain Text or HTML.
How to change default message format
Outlook 2010
- Select the File tab
- Click Options, then select Mail
- Look for Compose messages, Compose messages in this format
- Choose either HTML or Plain Text from the drop-down menu.
- Scroll down to Message format and look for When sending messages in Rich Text format to Internet recipients: and change to either Convert to HTML format or Convert to Plain Text format
- Click OK
Outlook 2003/2007
- On the Tools menu, click Options
- Click Mail Format
- In the Compose in this message format, select HTML or Plain Text
- Click Internet Format
- Look for When sending Outlook Rich Text messages to Internet recipients, use this format: and select either Convert to Plain Text format or Convert to HTML format
- Click OK
Changing specific addressbook entries
Outlook 2010
- Select Address Book
- Select the contact you would like to edit then click on File, then Properties
- Double-click on the email address then select the icon to View more options for interacting with this person and select Outlook Properties
- In the E-Mail Properties window, change the Internet format to Send Plain Text only
- Click on OK
Outlook 2003/2007
- Select Address Book
- Select the contact you would like to edit then click on File, then Properties
- Double-click on the email address
- In the E-Mail Properties dialog box, click Send Plain Text only under Internet Format
- Click on OK