Pigeonhole is the name of the project that adds support for the Sieve language
(RFC 5228) and the ManageSieve protocol (RFC 5804) to the Dovecot Secure
IMAP/POP3 Server.

Sieve language specification and scripts provide mail filtering capabilities on
the server side for individual users. Each user can edit and upload (using
ManageSieve) sieve scripts to filter mail based on supported Sieve language
extensions within pigeonhole.

The Pigeonhole project provides Sieve support as a plugin to Dovecot's Local
Delivery Agent (LDA). The ManageSieve protocol is provided is an additional
service, next to Dovecot's own POP3 and IMAP services.

To configure pigeonhole, use sieve and managesieve config files installed with
dovecot documentation. Copy 20-managesieve.conf and 90-sieve.conf files to
/etc/dovecot/conf.d and edit them according to your needs.

For additional help with configuration, see:

  http://wiki2.dovecot.org/Pigeonhole/Sieve
  http://wiki2.dovecot.org/Pigeonhole/ManageSieve