Settings to Prevent Sending Winmail.dat Files by Outlook

Outlook sends a winmail.dat attachment when it encodes email in Rich Text Format (RTF) using Transport Neutral Encapsulation Format (TNEF) encoding. Recipients using non-Microsoft email clients receive this file instead of the actual email content or attachments. To stop this, change the message format settings in Outlook or disable TNEF via the registry.

Procedure

1. Go to File > Options > Mail. In the Compose messages section, set Compose messages in this format to HTML or Plain Text.

2. Click Internet Format and select Convert to HTML format or Convert to Plain Text format.

3. Edit the registry. Open Registry Editor and navigate to the following key:

   HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences (The version number of Outlook 2013 is 15.0.)

   Go to Edit > New > DWORD Value.

   Name the value DisableTNEF and press Enter.

   Right-click DisableTNEF and click Modify.

   Enter 1 in the Value data field and click OK.

   Go to File > Exit to close Registry Editor.

Note

When sending email to a large number of recipients that exceeds the Outlook threshold, the preceding settings may not fully prevent winmail.dat attachments for all recipients.