Solr FTS Engine

Solr is a Lucene indexing server. Dovecot communicates to it using HTTP/XML queries.

The steps described in this page are tested for Solr 7.7.0. For other versions, this these steps may need to be adjusted.


Dovecot is not compiled with Solr FTS support by default. To enable it, you need to add the --with-solr parameter to your invocation of the configure script. You will also need to have libexpat installed, including development headers (typically from a separate development package). Configuration will fail if --with-solr is enabled while libexpat headers cannot be found. Older versions of Dovecot also required libcurl for Solr support, but recent versions of Dovecot include a custom HTTP client.


Solr Installation

First, the Solr server needs to be installed. Most operating systems will have packages for this. The latest version can be downloaded and installed from official website, and here are instructions to install 7.7.0 based on the howto How to Install Apache Solr 7.5 on Debian 9/8:

tar xzf solr-7.7.0.tgz solr-7.7.0/bin/ --strip-components=2
sudo bash ./ solr-7.7.0.tgz

To use Solr with Dovecot, it needs to configured specifically for use with Dovecot.

sudo -u solr /opt/solr/bin/solr create -c dovecot

The location of the files for the newly created instance on the filesystem varies between operating systems and installation methods. For example, in Archlinux, the config files are located in /opt/solr/server/solr/dovecot/conf and data files can be found in /opt/solr/server/solr/dovecot/data. When installed from tarball, these directories can be found in /var/solr/data/dovecot/.

Once the instance is created, you can start Solr. The means of starting, stopping and querying the status of the solr service varies between systems. For systemd, these commands are as follows:

sudo systemctl stop solr
sudo systemctl start solr
sudo systemctl status solr

By default, the Solr administration page for the newly created instance is located at <https://localhost:8983/solr/#/~cores/dovecot>. It can be used to check the status of the Solr instance. Configuration errors are often most conveniently viewed here. Solr also writes log files. For a tarball installation, these can be found at /var/solr/logs/.

Solr Configuration

There are three primary configuration files that need to be changed to accommodate the Dovecot FTS needs: the instance configuration file solrconfig.xml and the schema files schema.xml and managed-schema used by the instance. These files are both located in the conf directory of the Solr instance (e.g., /var/solr/data/dovecot/conf/).

Remove default core configuration files

rm -f /var/solr/data/dovecot/conf/schema.xml
rm -f /var/solr/data/dovecot/conf/managed-schema
rm -f /var/solr/data/dovecot/conf/solrconfig.xml

Install schema.xml and solrconfig.xml

Copy doc/solr-config-7.7.0.xml and doc/solr-schema-7.7.0.xml (Since Dovecot 2.3.6+) to /var/solr/data/dovecot/conf/ as solrconfig.xml and schema.xml. The managed-schema file is generated based on schema.xml.

Dovecot Plugin

See fts-solr plugin for setting information.

Example Configuration

mail_plugins = $mail_plugins fts fts_solr

plugin {
  fts = solr
  fts_solr = url=

Important notes:

  • Some mail clients will not submit any search requests for certain fields if they index things locally eg. Thunderbird will not send any requests for fields such as sender/recipients/subject when Body is not included as this data is contained within the local index.

Solr Commits & Optimization

Solr indexes should be optimized once in a while to make searches faster and to remove space used by deleted mails. Dovecot never asks Solr to optimize, so you should do this yourself. Perhaps a cronjob that sends the optimize-command to Solr every n hours.

With v2.2.3+ Dovecot only does soft commits to the Solr index to improve performance. You must run a hard commit once in a while or Solr will keep increasing its transaction log sizes. For example send the commit command to Solr every few minutes.

# Optimize should be run somewhat rarely, e.g. once a day
curl https://<hostname/ip>:<port|default 8983>/solr/dovecot/update?optimize=true
# Commit should be run pretty often, e.g. every minute
curl https://<hostname/ip>:<port|default 8983>/solr/dovecot/update?commit=true

You may not need those if you are using a recent Solr (7+) or SolrCloud. The default configuration of Solr is to auto-commit every once in a while (~15sec) so commit is not necessary. Also, the default TieredMergePolicy in Solr will automatically purge removed documents later, so optimize is not necessary.

Soft Commits

If soft commits are enabled, dovecot will perform a soft commit to Solr at the end of transaction. This has the benefit that search results are immediately available. You can also enable automatic commits in SOLR config, with


or setting it in solrconfig.xml with


Re-index mailbox

If you require to force dovecot to reindex a whole mailbox you can run the command shown, this will only take action when a search is done and will apply to the whole mailbox.

doveadm fts rescan -u <username>

If you want to index a single mailbox/all mailboxes you can run the command shown, this will happen immediately and will block until the action is completed.

doveadm index [-u <user>|-A] [-S <socket_path>] [-q] [-n <max recent>] <mailbox mask>

Sorting by relevancy

Solr/Lucene supports returning a relevancy score for search results. If you want to sort the search results by the score, use Dovecot’s non-standard X-SCORE sort key:

1 SORT (X-SCORE) UTF-8 <search parameters>


Dovecot creates the following fields:

  • id: Unique ID consisting of uid/uidv/user/box.

    • Note that your user names really shouldn’t contain ‘/’ character.

  • uid: Message’s IMAP UID.

  • uidv: Mailbox’s UIDVALIDITY. This changes if mailbox gets recreated.

  • box: Mailbox name

  • user: User name who owns the mailbox, or empty for public namespaces

  • hdr: Indexed message headers

  • body: Indexed message body

  • any: “Copy field” from hdr and body, i.e. searching based on this will search from both headers and bodies.

Lucene does duplicate suppression based on the “id” field, so even if Dovecot sends the same message multiple times to Solr it gets indexed only once. This might happen currently if multiple searches are started at the same time.

You might want to build a cronjob to go through the Lucene indexes once in a while to delete indexed messages (or entire mailboxes) that no longer exist on the filesystem. It shouldn’t normally find any such messages though.


# telnet localhost imap
1 login username password
2 select Inbox
3 SEARCH text "test"


If you have more users than fit into a single Solr box, you can split users off to different servers. A couple of different ways you could do it are:

  • Have some HTTP proxy redirecting the connections based on the URL

  • Configure Dovecot’s userdb lookup to return a different host for fts_solr setting using User database extra fields.

    • LDAP: user_attrs = ..., solrHost=fts_solr=url=https://%$:8983/solr/dovecot/

    • MySQL: user_query = SELECT concat('url=https://', solr_host, ':8983/solr/dovecot/') AS fts_solr, ...

You can also use SolrCloud, the clustered version of Solr, that allows you to scale up, and adds failover / high availability to your FTS system. Dovecot-solr works fine with a SolrCloud cluster as long as the solr schema is the right one.

External Tutorials

External sites with tutorials on using Solr under Dovecot


Some additional things which might help you configuring Solr search:

  • If you are using Tomcat: Set maxHttpHeaderSize="65536" (connector definition for port 8080 in /etc/tomcat7/server.xml) to accept long search query strings (iPhones tend to send multi-kilobyte-sized queries)

  • Set df to hdr in /etc/solr/conf/solrconfig.xml (/select request handler) to avoid strange undefined field text errors.

  • Please keep in mind that you will have to change the Solr URL to include the core name (ie: dovecot: https://localhost:8939/solr/dovecot).