What is email spoofing?
"Email Spoofing" is when someone uses your email address as the reply to email address in an email. Because the fields in Outlook Express, or any pop email client program for that matter, are not validated, any user can put any address they choose in this field. This will give the recipient the impression that it came from your email address, but in actuality it wasn't. Most email users fail to read the headers of the email which actually define the sending SMTP server, and if they were to read it and knew how to compare emails, they would find that it's not actually you who's sending the emails.
Unfortunately, there is no real prevention of this because of how easy it is to "spoof" someone's email address. Your domain may have been a target, but at the same time you may be a random victim of someone who is playing a prank. If you would like to further investigate this, we suggest that you notify your local ISP or local authorities and provide them with these bounce back notices, and then they should be able to trace where the email actually originated from.
3rd of July, 2013