The big problem is the likes of Yahoo and MSN email addresses, as long as EBAY and other sales sites allow users to use free and anonymous emails there will always be those who feel they can behave in this way.
It should be possible to track these people, but sadly there are so many of them, and a large majority are in third world countries, and anybody with a PC and an internet connection can set themselves up an email server, and generate a new batch of anonymous emails.
Were we to have someone with decent hacking skills then there would be ways of pinning these people down, but frankly my skills in this direction are limited, not to mention the fact that such actions are considered illegal.
