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.

Requires: dovecot

Configuration: sieve and managesieve config files are placed with
dovecot documentation.  Copy over 20-managesieve.conf and 90-sieve.conf
to /etc/dovecot/conf.d and edit accordingly.