SPAM Back-Scatter

The core of the back-scatter problem is that it is trivial to forge the sender address of an email; as the standard email protocols provide no mechanisms to authenticate the sender's email address. Spammers don't want to deal with backscatter, and they don't want complaints coming back; so they forge the sender address in spams they send out. However, while there are no truly standard and universal mechanisms to authenticate a sender's claimed email address, there are mechanisms to determine if an email address is valid or not.