Spam or ‘Junk Mail’ is where electronic spam is sent by email to innocent emails accounts. This spam is normally commercial emails that are trying to get the attention of certain users to attract them to certain sites, but spam can also contain disguised links which send the user to a false duplicate site where they become targets of phishing or malware. Botnets are networks of virus-infected computers that are the main source of the spam sending as they send about 80% of the spam.
A filtering solution applied to your email system uses a set of protocols to determine which of your incoming messages are spam and which aren’t. There are multiple filters:
Content filters review the content within the email to determine if its spam or not.
Header filter review the header of the email in search of falsified information.
General blacklist filters stop all emails that come from a blacklisted file of known spammers.
Spam was declared legal by the CAN-SPAM Act of 2003 if the spam provides the certain specifications, so it will never go away.