Some other methods of spam filtering

Other methods The general tightening of the requirements for letters and senders, for example ? refusing to accept letters with the wrong return address (letters from non-existent domain), check the domain name to IP-address, which is a letter, etc. Through these measures eliminated only most primitive spam ? a small number of messages. However, it is not zero, so the meaning of their use remains. Sort the letters on the contents of the letter header fields allows to get rid of a certain amount of spam. Some clients (eg, Mozilla Thunderbird or The Bat!) Provide an opportunity to examine the headers without downloading from the server all the email as well, and thus save bandwidth. System type ?a challenge-response? to verify that the sender ? the person, not