This article explains how to prevent winmail.dat attachments from being sent in Outlook. It applies to Outlook 2019, 2016, 2013, 2010, 2007, 2003; and Outlook for Microsoft 365. It includes information about disabling winmail.dat for specific recipients.
When Outlook sends a message with rich text formatting for bold text and other text enhancements, it includes the formatting commands in a winmail.dat file. Receiving e-mail clients that do not understand this code display it as an attachment. Outlook can also package other file attachments into the winmail.dat file.
You can remove winmail.dat completely by making Outlook stop sending emails via RTF.
To prevent Outlook from attaching a winmail.dat file when you send an email:
