An error occurred while saving the commentJX commented
To get around this issue, first drag and drop your image as per normal.
Thereafter, inspect the HTML code and replace the <img src="file://...
Covert your image to a base64 code using this: http://base64online.org/encode/
remeber to check Format As Data URL
with the encoded src="data:image/jpeg;base64,/9j/4Q.....
Meanwhile, a paid app should work as it is described - just drag and drop. Looks like Airmail embedding images needs work.