what u do is this - when you receive it - look for the address it came from - or the return to address - lets say it came from
somewhere@yahoo.com, all you have to do is forward the email to
abuse@yahoo.com - or if it came from
somewhere@hotmail.com - do the same thing, forward the email to
abuse@hotmail.com.
Sometimes the from email address is a fake one, but in the body of the email, the writer will write something like - reply to so so and so email - then do the same thing as above - forward it to the abuse address of the email.
All email programmes has their own abuse email which u can always forward to - you will receive a reply, and in most cases, they block the email address.