Dovecot Dictionary (dict)

Dovecot's lib-dict can be used to access simple key-value databases. This is used by, for example, last-login plugin and imap_metadata.

The dictionaries can be accessed either directly by the mail processes or they can be accessed via proxy processes.

Currently supported backends are:

Name	Description
file	Flat Files
fs	FS (lib-fs wrapper)
ldap	LDAP (read only)
proxy	Proxy
redis	Redis
sql	SQL

Connection Pooling

The sql driver keeps a maximum of 10 unused SQL connections open (infinitely) and reuses them for SQL dict lookup requests.

The dict server process keeps the last 10 idle dict backends cached for maximum of 30 seconds. Practically this acts as a connection pool for redis and ldap. Note that this doesn't affect sql, because it already had its own internal cache.

Backends

Flat Files

file:<path>

The file will simply contain all the keys that are used. Not very efficient for large databases, but good for small ones such as a single user's quota.

Filesystem (lib-fs-wrapper)

fs:<driver>:<driver args>

This is a wrapper for lib-fs, which most importantly has the posix backend. So using:

fs:posix:prefix=/var/lib/dovecot/dict/

Would create a separate file under /var/lib/dovecot/dict for each key.

LDAP

LDAP support is very similar to sql support, but there is no write support.

Note that the LDAP backend must be used via proxy.

See LDAP authentication.

Configuration

dovecot.conf

dict {
  somedict = ldap:/path/to/dovecot-ldap-dict.conf.ext
}

LDAP Parameters

Parameter	Required	Description
uri	YES	LDAP connection URI as expected by OpenLDAP.
bind_dn	NO	DN or upn to use for binding. (default: none)
debug	NO	Enable debug. 0 = off (default), 1 = on.
password	NO	Password to use, only SIMPLE auth is supported at the moment. (default: none)
timeout	NO	How long to wait for reply, in seconds. (default:30 seconds)
tls	NO	Use TLS? yes: Require either ldaps or successful start TLS try: Send start TLS if necessary (default) no: Do not send start TLS.

Examples

To map a key to a search:

map {
  pattern = priv/test/mail
  filter = (mail=*)  # the () is required
  base_dn = ou=container,dc=domain
  username_attribute = uid # default is cn
  value_attribute = mail
}

To do a more complex search:

map {
  pattern = priv/test/mail/$location
  filter = (&(mail=*)(location=%{location}) # the () is required
  base_dn = ou=container,dc=domain
  username_attribute = uid # default is cn
  value_attribute = mail

  fields {
    location=$location
  }
}

Proxy

proxy:[param=value:...][<dict path>]:<destination dict>

Proxying is used to perform all dictionary accessing via the dict processes. (The dict processes exist only if dict proxying is used.) This is especially useful with backends where their initialization is relatively expensive, such as SQL. The dict processes will perform connection pooling.

If <dict path> is specified, it points to the socket where the dict server is answering. The default is to use $base_dir/dict. Usually this is changed to dict-async if the dict backend support asynchronous lookups (e.g. ldap, pgsql, cassandra). The dict-async service allows more than one client, so this configuration prevents creating unnecessarily many dict processes.

The <destination dict> contains the dict name in the dict { .. } settings. For example: proxy:dict-async:quota.

See proxy processes for more information about the dict server.

Proxy Parameters

Parameter	Required	Description
idle_timeout=<time_msecs>	NO	How long to idle before disconnecting. Default: 0, which means immediate disconnect after finishing the operation. Added: 3.0.0
slow_warn=<time_msecs>	NO	Log a warning about lookups that take longer than this interval. Default: 5s. Added: 3.0.0

Redis

redis:param=value:param2=value2:...

Note that Redis backend is recommended to be used via proxy to support connection pooling.

WARNING

Currently using Redis without proxying may cause crashes.

Redis Parameters

Parameter	Required	Description
db	NO	Database number (default: 0)
expire_secs	NO	Expiration value for all keys (in seconds) (default: no expiration)
host	NO	Redis server host (default: 127.0.0.1)
port	NO	Redis server port (default: 11211)
password	NO	Redis Password (default: none)
prefix	NO	Prefix to add to all keys (default: none)
timeout_msecs	NO	Abort lookups after specified number of milliseconds (default: 30000)

SQL

<sql driver>:<path to dict-sql config>

The <sql driver> component contains the SQL driver name, such as mysql, pgsql, sqlite, or cassandra.

WARNING

Note that the SQL backend must be used with proxy.

The dict-sql config file consists of SQL server configuration and mapping of keys to SQL tables/fields.

See SQL authentication database.

SQL Connect String

connect = host=localhost dbname=mails user=sqluser password=sqlpass

The connect setting is exactly the same as used for SQL authentication database.

SQL Mapping

SQL mapping is done with a dict key pattern and fields. When a dict lookup or update is done, Dovecot goes through all the maps and uses the first one whose pattern matches the dict key.

For example when using dict for a per-user quota value the map looks like:

map {
  pattern = priv/quota/storage
  table = quota
  username_field = username
  value_field = quota_bytes
}

• The dict key must match exactly priv/quota/storage. The dict keys are hardcoded in the Dovecot code, so depending on what functionality you're configuring you need to know the available dict keys used it.

• This is a private dict key (priv/ prefix), which means that there must be a username_field. The username_field is assumed to be (at least part of) the primary key. In this example we don't have any other primary keys.

• With MySQL the above map translates to SQL queries:

  • SELECT quota_bytes FROM quota WHERE username = '$username_field'
  • INSERT INTO quota (username, quota_bytes) VALUES ('$username_field', '$value') ON DUPLICATE KEY UPDATE quota_bytes='$value'

You can also access multiple SQL fields. For example acl_shared_dict can contain:

map {
  pattern = shared/shared-boxes/user/$to/$from
  table = user_shares
  value_field = dummy

  fields {
    from_user = $from
    to_user = $to
  }
}

• The acl_shared_dict always uses 1 as the value, so here the value_field is called dummy.

• The SQL from_user and to_user fields are the interesting ones. Typically the extra fields would be part of the primary key.

• With MySQL the above map translates to SQL queries:

  • SELECT dummy FROM user_shares WHERE from_user = '$from' AND to_user = '$to'
  • INSERT INTO user_shares (from_user, to_user, dummy) VALUES ('$from', '$to', '$value') ON DUPLICATE KEY UPDATE dummy='$value'

SQL dict with mail_attribute_dict

It's possible to implement mail_attribute_dict also with SQL dict.

WARNING

Using shared attributes in mail_attribute_dict requires the mailbox GUID to be unique between users. This is not the case when mails were migrated via imapc, because it uses a hash of the mailbox name as the GUID. So every migrated user would have exactly the same INBOX GUID, preventing the use of dict-sql. It is currently not possible to add a username as an additional unique identifier.

# CREATE TABLE mailbox_private_attributes (
#   username VARCHAR(255),
#   mailbox_guid VARCHAR(32),
#   attr_key VARCHAR(255),
#   value TEXT,
#   PRIMARY KEY (username, mailbox_guid, attr_key)
# )
map {
  pattern = priv/$mailbox_guid/$key
  table = mailbox_private_attributes
  username_field = user
  value_field = value

  fields {
    attr_key = $key
    mailbox_guid = $mailbox_guid
  }
}

# CREATE TABLE mailbox_shared_attributes (
#   mailbox_guid VARCHAR(32),
#   attr_key VARCHAR(255),
#   value TEXT,
#   PRIMARY KEY (mailbox_guid, attr_key)
# );
map {
  pattern = shared/$mailbox_guid/$key
  table = mailbox_shared_attributes
  value_field = value

  fields {
    attr_key = $key
    mailbox_guid = $mailbox_guid
  }
}

Dictionary Proxy Process

Dict server is used for providing dictionary access via server processes instead of doing it directly from whichever process wants to access the dictionary. This is useful for some backends with relatively high connection cost (e.g. sql), but not necessarily for others (e.g., redis.

When a mail process uses the dict proxy, it needs to have access the dict UNIX socket. By default only the dovecot user has access to the dict socket, which doesn't typically work in any installation. However, giving too wide permissions by default might allow untrusted users to access the dict and cause problems.

If all users share a single UNIX UID (e.g. vmail), you could make the dict socket accessible only to it:

service dict {
  unix_listener dict {
    mode = 0600
    user = vmail
  }
}

If you use multiple UNIX UIDs, you can add an extra group for all Dovecot mail processes. This works even if you have untrusted system users who have shell access to the server:

mail_access_groups = dovecot

service dict {
  unix_listener dict {
    mode = 0660
    group = dovecot
  }
}

However, it works with LDA only if it's started as root. If this isn't possible, use LMTP Server instead.