I would be fine if my client would neatly format a limited markdown format and other clients supported entering it in a WYSIWYG fashion, as long as all the disp

I would be fine if my client would neatly format a limited markdown format and other clients supported entering it in a WYSIWYG fashion, as long as all the displayed content is part of the transmitted message (no further connection to the net) and the client is guaranteed not to execute any sender-supplied code or transmit any data when links or images are displayed.