One of Cyrus IMAP's more sophisticated features is the ability to create indexes of messages and mailboxes to allow fast searching of headers and message text.

The indexing is done using squatter, and is best achieved by launching it at regular intervals from cyrus.conf:

EVENTS {
...
# indexing of mailboxs for server side fulltext searches
# reindex changed mailboxes (fulltext) approximately every other hour
squatter_1 cmd="nice -n 19 squatter -s" period=120
# reindex all mailboxes (fulltext) daily
squatter_a cmd="squatter" at=0517
...
}

Once the indexes have been created, the improvement in search performance is dramatic.