Sieve is a formal language for email filtering. It allows end users to execute certain actions on incoming emails (e.g., move message into folder ‘foobar’) if they satisfy certain criteria (e.g., sender is ‘firstname.lastname@example.org’).
See also sieve.info
Email filter rules are among the most powerful mechnisms for users to automate processing of their email. This is also indicated by a large number of extensions.
Filtering criteria are mostly tied to structural elements of an email (e.g., date, size) and low-level textual identifiers such as email addresses (
email@example.com) or keywords matching email body text.