You can change a plain text message to HTML.

  1. In the message, click Reply, Reply All, or Forward.

  2. If you’re working in the Reading Pane, click Pop Out.

  3. In the message window, click Format Text > HTML.

    HTML format option on the Format text tab in a message

Other options

  • If you want to change the message to Rich Text Format, click Rich Text.


Outlook will now allow you to send the email




https://support.microsoft.com/en-us/office/change-the-message-format-to-html-rich-text-format-or-plain-text-338a389d-11da-47fe-b693-cf41f792fefa