The official name of 'Spam' is unsolicited commercial email and it is a major pest. It is estimated that as much as 80% of all email traffic is spam.
To reduce this burden, the Internet Service Providers (ISP) have anti-spam filters in place on their networks that try and spot spam and then block it.
There is no perfect system, as the spam-senders are constantly battling to find ways around them. For example, a filter may look for certain key words within the email - so the spammers send text images instead or they deliberately mis-spell or mangle words that humans can read, but machines cannot.
Anti-spam filters work by following a set of rules that together decide whether or not an email is spam. They also have black-lists of IP addresses that are known to issue spam. There are 'Baysean Filters' and 'Heuristic Filters' that try to learn as they pick up more and more spam. But unfortunately some still gets through.
You can rent email services that offer to filter spam for you. The dodgy emails are re-directed to a 'Bulk box'. Then it is up to you to check if any proper emails ended up there as well.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: Anti-spam filter