Jul 31 19:26:40 mail dovecot: imap(user@mx.domain): Error: Dictionary URI is missing ':': quota
Jul 31 19:26:40 mail dovecot: imap(user@mx.domain): Error: user user@mx.domain: Initialization failed: Failed to initialize quota: Quota root storage=0 proxy: init() failed
Jul 31 19:26:40 mail dovecot: imap(user@mx.domain): Error: Invalid user settings. Refer to server log for more information.

dovecot version: 1:2.0.13-1ubuntu2

dovecot.conf:

disable_plaintext_auth = no
dotlock_use_excl = yes
first_valid_gid = 8
first_valid_uid = 8
last_valid_gid = 8
last_valid_uid = 8
login_greeting = Mail Server Ready.
mail_location = maildir:/home/vmail/%d/%n
mail_privileged_group = mail
passdb {
        args = /etc/dovecot/dovecot-sql.conf
        driver = sql
}
protocols = imap pop3
service auth {
        unix_listener /var/spool/postfix/private/auth {
                group = postfix
                mode = 0660
                user = postfix
        }
        user = root
}
ssl_cert = </etc/ssl/private/crt.pem
ssl_key = </etc/ssl/private/crt.pem
userdb {
        args = /etc/dovecot/dovecot-sql.conf
        driver = sql
}
verbose_proctitle = yes
protocol imap {
        imap_client_workarounds = delay-newmail tb-extra-mailbox-sep
        mail_plugins = quota imap_quota
}
protocol pop3 {
        mail_plugins = quota
        pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
        pop3_uidl_format = %08Xu%08Xv
}
protocol lda {
        mail_plugins = quota
        postmaster_address = postmaster@mx.domain.de
        sendmail_path = /usr/sbin/sendmail
}
dict {
        quotadict = mysql:/etc/dovecot/dovecot-dict-quota.conf
}
plugin {
        quota = dict:user::proxy::quotadict
}
!include conf.d/10-logging.conf


/etc/dovecot/dovecot-dict-quota.conf:
driver = mysql
connect = host=localhost dbname=postfix user=postfix password=password
default_pass_scheme = MD5
table = quota2
select_field = current
where_field = path
username_field = username

# HERE I dont know if that is correct, as the quota2 table created by postfixadmin has different row
# names:
# username, bytes and messages ..


/etc/dovecot/dovecot-sql.conf
driver = mysql
connect = host=localhost dbname=postfix user=postfix password=password
default_pass_scheme = MD5
password_query = SELECT password FROM mailbox WHERE username = '%u'
user_query = SELECT maildir, 8 AS uid, 8 AS gid, CONCAT('dict:storage=',floor(quota/1000),' proxy::quota') as quota FROM mailbox WHERE username = '%u' AND active='1'