Editing Anti-spam techniques (section)

===Rule-based filtering===
{{Further|Email filtering}}

Content filtering techniques rely on the specification of lists of words or [[regular expression]]s disallowed in mail messages. Thus, if a site receives spam advertising "herbal Viagra", the administrator might place this phrase in the filter configuration. The mail server would then reject any message containing the phrase.

Header filtering looks at the header of the email which contains information about the origin, destination and content of the message. Although spammers will often [[Spoofing attack|spoof]] fields in the header in order to hide their identity, or to try to make the email look more legitimate than it is, many of these spoofing methods can be detected, and any violation of, e.g., {{IETF RFC|5322|7208}}, standards on how the header is to be formed can also serve as a basis for rejecting the message.