This article explains how to set the default message format in Outlook. Instructions apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Microsoft 365.
HTML is the default message format in Outlook. Although plain text format works for all email programs, it does not support text formatting. Rich Text Format (RTF) is supported only by Microsoft Exchange Client versions 4.0 and 5.0 and Outlook.
To configure the default format for new emails in Outlook, follow these steps:
Go to File > Options.