Look at this link http://sherwoodhosting.com/email-ftp-support/email-address-hijacking-forgery.html
Also this is from a question and answer sight.
"When you receive a Mailor Daemon failure notice it's caused by a spammer to hide their address, it's called "spoofing" They are looking for a good working address. Just delete them. Never mark them as Spam, because you will be spamming your own address