From what you have shared above,If I understand correctly you are willing to add a Rich text image or company logo in the message box shown in picture below?
logo you can try with the steps mention below, but Rich Text can not be send.
Hope this helps, and let us know if this isn't what you were referring to.
The logo and color appear at the top of the recipient's email, almost like a title. I want to be able to include an email message with my regular company signature at the bottom, just like I would with any other email. Other ideas?
What you have mentioned in your last message, that functionality is currently unavailable. This is correct that the logo that you will be adding that will display in the subject of the email at receiver's end.