Ubuntu – Setup Postfix+Dovecot reading from database

I'm trying to setup Postfix and Dovecot, the latter with virtual users stored in a MySQL database, following this guide (but here I recap everything as there are some "bugs" in the guide I fixed following the comments). Preamble: I have Postfix, Dovecot, postfix-mysql and dovecot-mysql installed from Ubuntu repositories.

Let's start with Postfix config:

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no   
readme_directory = no

myhostname = localhost
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = localhost
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all

relay_domains = *
virtual_alias_maps = proxy:mysql:/etc/postfix/virtual_alias_maps.cf
virtual_mailbox_domains = proxy:mysql:/etc/postfix/virtual_mailbox_domains.cf
virtual_mailbox_maps = proxy:mysql:/etc/postfix/virtual_mailbox_maps.cf
virtual_mailbox_base = /home/vmail
virtual_mailbox_limit = 512000000
virtual_minimum_uid = 5000
virtual_transport = virtual
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
local_transport = virtual
local_recipient_maps = $virtual_mailbox_maps
transport_maps = hash:/etc/postfix/transport

smtpd_sasl_auth_enable = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = /var/run/dovecot/auth-client
smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
smtpd_sasl_security_options = noanonymous
smtpd_sasl_tls_security_options = $smtpd_sasl_security_options
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/ssl/private/server.crt
smtpd_tls_key_file = /etc/ssl/private/server.key
smtpd_sasl_local_domain = $myhostname
broken_sasl_auth_clients = yes
smtpd_tls_loglevel = 1

Then I created user vmail to store emails:

groupadd -g 5000 vmail
useradd -u 5000 -g vmail -s /usr/bin/nologin -d /home/vmail -m vmail

And MySQL database and user to store info about domains and virtual users:

CREATE DATABASE postfix_db;
USE postfix_db;
CREATE USER postfix_user@localhost IDENTIFIED BY 'password';
GRANT ALL ON postfix_db.* TO postfix_user@localhost;
FLUSH PRIVILEGES;

Then I created the tables related to domains, forwardings and users:

CREATE TABLE `domains` (
  `domain` varchar(50) NOT NULL default "",
  PRIMARY KEY  (`domain`),
  UNIQUE KEY `domain` (`domain`)
);


CREATE TABLE `forwardings` (
  `source` varchar(80) NOT NULL default "",
  `destination` text NOT NULL,
  PRIMARY KEY  (`source`)
);

CREATE TABLE `users` (
  `email` varchar(80) NOT NULL default "",
  `password` varchar(20) NOT NULL default "",
  `quota` varchar(20) NOT NULL default '20971520',
  `domain` varchar(255) NOT NULL default "",
  UNIQUE KEY `email` (`email`)
);

I added my domain (which has A and MX records properly set) in the table:

INSERT INTO `domains` VALUES ('virtualdomain.tld');

And an account related to that domain:

INSERT INTO `users` VALUES ('info@virtualdomain.tld', ENCRYPT('password'), '20971520', 'virtualdomain.tld');

Then I created a self-signed cert:

cd /etc/ssl/private/
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out server.key
chmod 400 server.key
openssl req -new -key server.key -out server.csr
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt
chmod 444 server.crt

And then the files I was referring to in Postfix config:

/etc/postfix/virtual_alias_maps.cf

user = postfix_user
password = hunter2
hosts = localhost
dbname = postfix_db
table = domains
select_field = domain
where_field = domain

/etc/postfix/virtual_mailbox_domains.cf

user = postfix_user
password = hunter2
hosts = localhost
dbname = postfix_db
table = forwardings
select_field = destination
where_field = source

/etc/postfix/virtual_mailbox_maps.cf

user = postfix_user
password = hunter2
hosts = localhost
dbname = postfix_db
table = users
select_field = concat(domain,'/',email,'/')
where_field = email

And then

touch /etc/postfix/transport
postmap /etc/postfix/transport

Now I deleted the default Dovecot config file, replacing it with:

protocols = imap
auth_mechanisms = plain
passdb {
    driver = sql
    args = /etc/dovecot/dovecot-sql.conf
}
userdb {
    driver = sql
    args = /etc/dovecot/dovecot-sql.conf
}

service auth {
    unix_listener auth-client {
        group = postfix
        mode = 0660
        user = postfix
    }
    user = root
}

mail_home = /home/vmail/%d/%u
mail_location = maildir:~

ssl_cert = </etc/ssl/private/server.crt
ssl_key = </etc/ssl/private/server.key

I created the /etc/dovecot/dovecot-sql.conf file:

driver = mysql
connect = host=localhost dbname=postfix_db user=postfix_user password=hunter2
# The new name for MD5 is MD5-CRYPT so you might need to change this depending on version
default_pass_scheme = MD5-CRYPT
# Get the mailbox
user_query = SELECT '/home/vmail/%d/%u' as home, 'maildir:/home/vmail/%d/%u' as mail, 5000 AS uid, 5000 AS gid, concat('dirsize:storage=',  quota) AS quota FROM users WHERE email = '%u'
# Get the password
password_query = SELECT email as user, password, '/home/vmail/%d/%u' as userdb_home, 'maildir:/home/vmail/%d/%u' as userdb_mail, 5000 as  userdb_uid, 5000 as userdb_gid FROM users WHERE email = '%u'
# If using client certificates for authentication, comment the above and uncomment the following
#password_query = SELECT null AS password, ‘%u’ AS user

… and finally restarted dovecot and postfix:

service postfix dovecot restart

The problem is that when I try to send an email to info@virtualdomain.tld, I see this in logs:

NOQUEUE: reject: RCPT from blablabla.com[xxx.xxx.xxx.xxx]: 451 4.3.0 <info@virtualdomain.tld>: Temporary lookup failure; from=<my@email.tld> to=<info@virtualdomain.tld> proto=ESMTP helo=<blablabla.com>

And the mail bounces back with the error

550 5.1.1 "Recipient address rejected: User unknown in virtual alias table"