Backscatter has become increasingly harmful because many servers are now listening and querying backscatter lists before accepting email.  With this now being seen and becoming more common place it is up to administrators to do what they can to prevent from being listed as a server who sends backscatter.  What is Backscatter you might ask, Backscatter is the sending of a Non-Delivery Report (NDR) to a sender who did not actually send the message being bounced. 

For example, a server receives a message from ceo@ebay.com that is addressed to an unknown account.  Since the account does not exist on the server it would normally send a bounce back to ceo@ebay.com letting them know this.  Unfortunately in this case the message was actually spoofed and the real owner of ceo@ebay.com never sent this message but still could possibly end up with an NDR that would then thoroughly confuse them.