anti-spam tools
fighting spam on different levels

Generally said, there are three different ways of fighting spam mails. They are utilized on the following levels:
  • Gateway Level:
    Gateway Filters work, as the name says, as a filter for a whole mail-domain. It's often a native application or a firewall add-on.
  • Server Level:
    Server filters join an increasing popularity. Similar to gateway filters server-side filters work on the mail server. See anti-relaying for more information.
  • Client Level:
    But also the end user can utilize anti-spam tools on their local workstations. They are often used as additional local security instance for the providers anti-spam mechanisms.
To ensure that these protections are working the right way, spam has to be detected as spam. This is why, spammer-lists are used, which contain addresses and domains. Using these criterias, a certain amount of spam mails can be filtered, theoretically. In reality the limitations of this system can be seen very fast: About 80 percent of all spammers are using faked headers and change them very often. The more secure way is hunting for keyword in the mail-body.