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Question/Problem Question/Problem
  Why am I receiving a large quantity of “Your mail could not be delivered” bounce notifications when I did not send messages to any of these recipients?
Answer/Resolution Answer/Resolution
 
It is more than likely that you are receiving what is commonly known as "backscatter" spam.  Backscatter occurs when a spammer "spoofs", or forges, your email address.   A spammer will send out a large quantity of email with your email address in the From: field and when this spam is rejected, you end up receiving these messages.  The messages are returned to you and not the original spammer because the original message's From: header is forged to contain your email address.
 
Example:
 
A spammer forges an email to look like it is from john@johndoe.com and sends it to mail@mailserver.com.
 
The mail server at mailserver.com sees that the message claims that it is from john@johndoe.com, and if no checks are run to validate that claim, the mail server will send a rejection message to john@johndoe.com
 
John checks his email the next morning and sees a bounced message that he never sent in the first place.
 
If a mail server is configured properly, it should run a series of checks to ensure that the mail is being sent from where it claims to be from.  An improperly configured server will not run checks to confirm that the sender is valid and will send a bounce back. 

Category : General
FAQ ID : 102
Last Updated : 1/5/2011