<<<what is the point of a blank email?>>>
An email which appears to be blank can actually contain HTML code with the page width and page height set to zero so that it is invisible. The BadTrans virus was transmitted via "apparently" blank emails and didn't even require an attachment to infect the PC.
Using a palmtop device which didn't support HTML mail (or PC viruses!), I was able to see the HTML code for the "invisible" page with its zero width and height.