You can send messages with HTML formatting in Outlook, but not everyone wants to receive that kind of email. As an alternative, you can send plain text emails that can be read by any computer and email client. The instructions in this article apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, Outlook for Microsoft 365, Outlook Online, and Outlook for Mac.
How to Change Message Format from HTML to Rich Text or Plain Text in Outlook – Office 365
Here's how to compose and send an email message using plain text in Outlook:
Go to the Home tab and select New Email. Or press Ctrl+N.
In the message window, go to the Format Text tab.
