An e-mail filtering language supported by the Cyrus IMAP daemon, and defined in RFC:3028. Think of it as procmail for human beings, since it seems to be actually readable and understandable six months after you've defined your filters.
Resources:
- What's left of the home page
- A quick overview via Celso Pinto (includes draft specs for the filtering language)
- avelsieve, a Squirrelmail plugin (via this post regarding enabling timsieved on Mac OS X).
- websieve