I'm still working on the implementation, but in the very near future you will be able to attach multipart related images in the message body by clicking the image attach icon in the html editor formatting bar. It may be possible for me to detect drag and drop in the body too, but I expect that will be a bit tricky or not possible. Have you come across any other web email clients that do allow you to attach MPR content in the body by just dragging it into the html editor? if so let me know which ones as I would like to have a look at them to see how they implement this :-)

Marijn