This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.

Dictionary quota

The dictionary quota backend supports both storage and messages quota limits. The current quota is kept in a dictionary. The available dictionaries are:

The plugin parameter format is:

# v1.0:
quota = dict:<quota limits> <dictionary URI>
# v1.1+:
quota = dict:<quota root name>:<user name>:<dictionary URI>

If user name is left empty, the logged in username is used (this is probably what you want).

v1.0 & v1.1

Example:

dict {
  quotadict = mysql:/etc/dovecot-dict-quota.conf
}

plugin {
  # v1.0: 10MB and 1000 messages quota limit
  quota = dict:storage=10240:messages=1000 proxy::quotadict

  # v1.1 + MySQL:
  quota = dict:user::proxy::quotadict
  quota_rule = *:storage=10M:messages=1000
}

The above example uses dictionary proxy process (see below), because SQL libraries aren't linked to all Dovecot binaries.

Example dovecot-dict-quota.conf:

# v1.0 and v1.1 only - v1.2 has different configuration
connect = host=localhost dbname=mails user=sqluser password=sqlpass
table = quota
select_field = current
where_field = path
username_field = username 

Create the table like this:

create table quota (
  username varchar(255) not null,
  path varchar(100) not null,
  current integer,
  primary key (username, path)
); 

v1.2+

dict {
  quotadict = mysql:/etc/dovecot-dict-sql.conf
}

plugin {
  # v1.2 + MySQL:
  quota = dict:user::proxy::quotadict
  # v1.2 + file:
  quota = dict:user::file:%h/Maildir/dovecot-quota

  quota_rule = *:storage=10M:messages=1000
}

The above SQL example uses dictionary proxy process (see below), because SQL libraries aren't linked to all Dovecot binaries. The file example accesses the file directly.

Example dovecot-dict-sql.conf:

# v1.2+ only:
connect = host=localhost dbname=mails user=sqluser password=sqlpass
map {
  pattern = priv/quota/storage
  table = quota
  username_field = username
  value_field = bytes
}
map {
  pattern = priv/quota/messages
  table = quota
  username_field = username
  value_field = messages
}

Create the table like this:

CREATE TABLE quota (
  username varchar(100) not null,
  bytes bigint not null default 0,
  messages integer not null default 0,
  primary key (username)
);

If you're using PostgreSQL, you'll need a trigger:

CREATE OR REPLACE FUNCTION merge_quota() RETURNS TRIGGER AS $$
BEGIN
  IF exists(SELECT 1 FROM quota WHERE username = NEW.username) THEN
    UPDATE quota SET bytes = bytes + NEW.bytes,
      messages = messages + NEW.messages
      WHERE username = NEW.username;
    RETURN NULL;
  ELSE
    RETURN NEW;
  END IF;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER mergequota BEFORE INSERT ON quota
   FOR EACH ROW EXECUTE PROCEDURE merge_quota();

v1.0 Inaccuracy problems

With Dovecot v1.1+ quota is tracked accurately. With v1.0 you may have a problem:

If two IMAP clients do an expunge at the same time, the quota is reduced twice as much. Maildir++ backend also has the same problem, but it's not that big of a problem with it because it recalculates the quota once in a while anyway. Dict quota is recalculated only if the quota goes below zero (v1.0.rc30+ only).

So either you'll have to trust your users not to abuse this problem, or you could create a nightly cronjob to delete all rows from the SQL quota table to force a daily recalculation. The recalculation will of course slow down the server.

Dictionary proxy server

To avoid each process making a new SQL connection, you can make all dictionary communications go through a dictionary server process which keeps the connections permanently open.

The dictionary server is referenced with URI proxy:<dictionary server socket path>:<dictionary name>. The socket path may be left empty if you haven't changed base_dir setting in dovecot.conf. Otherwise set it to <base_dir>/dict-server. The dictionary names are configured in dovecot.conf. For example:

dict {
  quota = mysql:/etc/dovecot-dict-quota.conf
  expire = mysql:/etc/dovecot-dict-expire.conf
}