Try the following way:
1. Add Office 365 Outlook connection,
2. Add HtmlInput control, under the HtmlText property, input with the line below:
"Show your <b><font color=blue>HTML</font></b> text here.
<img src=""https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTf8peeAQ8Jbw4lowjdYM9OYVJFJr8EwgGNTsJ6BtbqPdNHWz2m""
alt=""Testing"" width=""500"" height=""100"">"
Things to mind is, when using the img tag within the HTMLText control, we need to add double quotes twice where it needs a double quote.
3. Add a button, then sepcify the following code example, make sure the IsHtml has been configured to true:
Office365.SendEmail("123@test.com","Testing",HtmlText1.HtmlText,{IsHtml:true})
The results:

Regards,
Michael