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:

MySQL (v1.0+)
PostgreSQL (v1.1.2+)
Flat file (v1.2.alpha3+)

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). The value of user name can be configured by using a Variable.

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 + SQL:
  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 bigint,
  primary key (username, path)
);

If you're using PostgreSQL, you'll need a trigger (don't forget 'CREATE LANGUAGE plpgsql'). Note that this trigger may still fail if two processes do the initial INSERT at the same time, v1.2+ fixes this.

CREATE OR REPLACE FUNCTION merge_quota() RETURNS TRIGGER AS $merge_quota$
BEGIN
  UPDATE quota SET current = NEW.current + current WHERE username = NEW.username AND path = NEW.path;
  IF found THEN
    RETURN NULL;
  ELSE
    RETURN NEW;
  END IF;
END;
$merge_quota$ LANGUAGE plpgsql;

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

v1.2+

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

plugin {
  # v1.2 + SQL:
  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)
);

The following is an example user_query from dovecot-mysql.conf to make use of the dict backend:

user_query = SELECT [path_to_homedir] AS home, [uid] AS uid, [gid] AS gid, CONCAT('*:bytes=', CAST(quota AS CHAR)) AS quota_rule FROM mailbox WHERE username = '%u' AND active = '1'

MySQL uses the following queries to update the quota. You need suitable privileges.

INSERT INTO table (bytes,username) VALUES ('112497180','foo@spam.dom') ON DUPLICATE KEY UPDATE bytes='112497180';
INSERT INTO table (messages,username) VALUES ('1743','foo@spam.dom') ON DUPLICATE KEY UPDATE messages='1743';
UPDATE table SET bytes=bytes-14433,messages=messages-2 WHERE username = 'foo@spam.dom';

If you're using PostgreSQL, you'll need a trigger (v1.2.beta1+):

CREATE OR REPLACE FUNCTION merge_quota() RETURNS TRIGGER AS $$
BEGIN
  IF NEW.messages < 0 OR NEW.messages IS NULL THEN
    -- ugly kludge: we came here from this function, really do try to insert
    IF NEW.messages IS NULL THEN
      NEW.messages = 0;
    ELSE
      NEW.messages = -NEW.messages;
    END IF;
    return NEW;
  END IF;

  LOOP
    UPDATE quota SET bytes = bytes + NEW.bytes,
      messages = messages + NEW.messages
      WHERE username = NEW.username;
    IF found THEN
      RETURN NULL;
    END IF;

    BEGIN
      IF NEW.messages = 0 THEN
        INSERT INTO quota (bytes, messages, username)
          VALUES (NEW.bytes, NULL, NEW.username);
      ELSE
        INSERT INTO quota (bytes, messages, username)
          VALUES (NEW.bytes, -NEW.messages, NEW.username);
      END IF;
      return NULL;
    EXCEPTION WHEN unique_violation THEN
      -- someone just inserted the record, update it
    END;
  END LOOP;
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
}

Insert used quotas to the new table after upgrade to 1.2.x

To fetch the quota of all accounts and write them to the database, any account needs to be accessed (you can just wait until all users have logged in once). To re-create the entries automatically, you can use this script (modify it to your needs). Basically it iterates over a list of email addresses fetched from the database and executes "x GETQUOTAROOT Inbox" for each account.

SQL="select email from mail_accounts where enabled=1"

LINES=$( echo $SQL | /usr/bin/mysql -u mail --password=?????????? mail )

for M in $LINES; do
  if [ $M != "email" ]; then
    echo "x GETQUOTAROOT Inbox" | USER=$M /usr/sbin/dovecot --exec-mail imap
  fi
done