Full-Text Search

Overview

Full-text search allows all messages to be indexed, so that mail clients can quickly and efficiently search messages by their full text content. Dovecot supports a variety of community supported FTS indexing backends.

docker-mailserver comes pre-installed with two plugins that can be enabled with a dovecot config file.

Please be aware that indexing consumes memory and takes up additional disk space.

Xapian

The dovecot-fts-xapian plugin makes use of Xapian. Xapian enables embedding an FTS engine without the need for additional backends.

The indexes will be stored as a subfolder named xapian-indexes inside your local mail-data folder (/var/mail internally). With the default settings, 10GB of email data may generate around 4GB of indexed data.

While indexing is memory intensive, you can configure the plugin to limit the amount of memory consumed by the index workers. With Xapian being small and fast, this plugin is a good choice for low memory environments (2GB) as compared to Solr.

Setup

To configure fts-xapian as a dovecot plugin, create a file at docker-data/dms/config/dovecot/fts-xapian-plugin.conf and place the following in it:

mail_plugins = $mail_plugins fts fts_xapian

plugin {
    fts = xapian
    fts_xapian = partial=3 full=20 verbose=0

    fts_autoindex = yes
    fts_enforced = yes

    # disable indexing of folders
    # fts_autoindex_exclude = \Trash

    # Index attachements
    # fts_decoder = decode2text
}

service indexer-worker {
    # limit size of indexer-worker RAM usage, ex: 512MB, 1GB, 2GB
    vsz_limit = 1GB
}

# service decode2text {
#     executable = script /usr/libexec/dovecot/decode2text.sh
#     user = dovecot
#     unix_listener decode2text {
#         mode = 0666
#     }
# }

adjust the settings to tune for your desired memory limits, exclude folders and enable searching text inside of attachments

Update docker-compose.yml to load the previously created dovecot plugin config file:

  version: '3.8'
  services:
    mailserver:
      image: docker.io/mailserver/docker-mailserver:latest
      container_name: mailserver
      hostname: mail
      domainname: example.com
      env_file: mailserver.env
      ports:
        - "25:25"    # SMTP  (explicit TLS => STARTTLS)
        - "143:143"  # IMAP4 (explicit TLS => STARTTLS)
        - "465:465"  # ESMTP (implicit TLS)
        - "587:587"  # ESMTP (explicit TLS => STARTTLS)
        - "993:993"  # IMAP4 (implicit TLS)
      volumes:
        - ./docker-data/dms/mail-data/:/var/mail/
        - ./docker-data/dms/mail-state/:/var/mail-state/
        - ./docker-data/dms/mail-logs/:/var/log/mail/
        - ./docker-data/dms/config/:/tmp/docker-mailserver/
        - ./docker-data/dms/config/dovecot/fts-xapian-plugin.conf:/etc/dovecot/conf.d/10-plugin.conf:ro
        - /etc/localtime:/etc/localtime:ro
      restart: always
      stop_grace_period: 1m
      cap_add:
        - NET_ADMIN

Recreate containers:

docker-compose down
docker-compose up -d

Initialize indexing on all users for all mail:

docker-compose exec mailserver doveadm index -A -q \*

Run the following command in a daily cron job:
```
docker-compose exec mailserver doveadm fts optimize -A
```
Or like the Spamassassin example shows, you can instead use cron from within docker-mailserver to avoid potential errors if the mail-server is not running:

Example

Create a system cron file:

# in the docker-compose.yml root directory
mkdir -p ./docker-data/dms/cron # if you didn't have this folder before
touch ./docker-data/dms/cron/fts_xapian
chown root:root ./docker-data/dms/cron/fts_xapian
chmod 0644 ./docker-data/dms/cron/fts_xapian

Edit the system cron file nano ./docker-data/dms/cron/fts_xapian, and set an appropriate configuration:

# Adding `MAILTO=""` prevents cron emailing notifications of the task outcome each run
MAILTO=""
#
# m h dom mon dow user command
#
# Everyday 4:00AM, optimize index files
0  4 * * * root  doveadm fts optimize -A

Then with docker-compose.yml:

services:
  mailserver:
    image: docker.io/mailserver/docker-mailserver:latest
    volumes:
      - ./docker-data/dms/cron/fts_xapian:/etc/cron.d/fts_xapian

Solr

The dovecot-solr Plugin is used in conjunction with Apache Solr running in a separate container. This is quite straightforward to setup using the following instructions.

Solr is a mature and fast indexing backend that runs on the JVM. The indexes are relatively compact compared to the size of your total email.

However, Solr also requires a fair bit of RAM. While Solr is highly tuneable, it may require a bit of testing to get it right.

Setup

docker-compose.yml:

  solr:
    image: lmmdock/dovecot-solr:latest
    volumes:
      - ./docker-data/dms/config/dovecot/solr-dovecot:/opt/solr/server/solr/dovecot
    restart: always

  mailserver:
    depends_on:
      - solr
    image: docker.io/mailserver/docker-mailserver:latest
    ...
    volumes:
      ...
      - ./docker-data/dms/config/dovecot/10-plugin.conf:/etc/dovecot/conf.d/10-plugin.conf:ro
    ...

./docker-data/dms/config/dovecot/10-plugin.conf:

mail_plugins = $mail_plugins fts fts_solr

plugin {
  fts = solr
  fts_autoindex = yes
  fts_solr = url=http://solr:8983/solr/dovecot/
}

Recreate containers: docker-compose down ; docker-compose up -d
Flag all user mailbox FTS indexes as invalid, so they are rescanned on demand when they are next searched: docker-compose exec mailserver doveadm fts rescan -A

Further Discussion

See #905