Full text search indexing

The following FTS indexers (in preferred order) are supported:

Solr communicates with Lucene's Solr server.
Lucene uses Lucene's C++ library. (Requires v2.1+)
Squat is Dovecot's own search index. (Obsolete in v2.1+)

Indexing

Currently the FTS indexes are updated only while searching, so neither the LDA nor an IMAP APPEND command updates the indexes immediately. This means that if user has received a lot of mail since the last indexing (== search operation), it may take a while to index all the mails before replying to the search command. Dovecot sends periodic "* OK Indexed n% of the mailbox" updates which can be caught by webmail implementations to implement a progress bar.

The indexing can be done manually (e.g. cronjob) or by a LDA script by running:

v2.1: doveadm index -u user@domain -q INBOX
v2.0: printf "a select INBOX\nb search text xyzzy\nc logout\n" | /usr/local/libexec/dovecot/imap -u user@domain

Of course the INBOX needs to be replaced with whatever mailbox needs to be indexed.

Rescan (v2.1+)

Since v2.1 Dovecot keeps track of indexed messages in the dovecot.index files. If this becomes out of sync with the actual FTS indexes (either too many or too few mails), you'll need to do a rescan:

doveadm fts rescan -u user@domain

Settings (v2.1+)

fts_index_timeout: When SEARCH notices that index isn't up to date, it tells indexer to index the mails and waits until it is finished. This setting adds a maximum timeout to this wait. If the timeout is reached, the SEARCH fails with: NO [INUSE] Timeout while waiting for indexing to finish
fts_decoder: Decode attachments to plaintext using this service and index the resulting plaintext.