Those emails are normally sent to the 'admin' user, so try just sending a plain old email to 'admin@yourdomain' and see if you get that 4 times. Then you know it must be some configuration issue somewhere - have you got your admin emails redirected somewhere to a group name ? Log in to webmail using the 'admin' account and see if it's in there four times.
I am assuming the emails are all exactly the same, there's not a slight change to a file name in each one... Are they all the same timestamp ?