replication and backend vpopmail

[Havrla]

Heloo, please

I need "replicate" dovecot / dsync.

Prerequisite:
doveadm  user   '*'

[Root @ joe ~] # doveadm user '' '
Error: User listing Returned failure
Fatal: user listing failed

It probably does not work because I have:
userdb{
    args = cache_key =% u quota_template quota_rule = = *: backend = q%
    driver = vpopmail
}

The manual is written:
iterate_query = SELECT email as user FROM mail_user

But does not specify how to connect to MySQL database if vpopmail

How to do it ?

To make it simple, vpopmail domain = DB table example domain example.com 
= table example_com

[root at franta ~]# mysql vpopmail
MariaDB [vpopmail]> desc lhotkanet_cz;
+-----------------+-----------+------+-----+---------+-------+
| Field           | Type      | Null | Key | Default | Extra |
+-----------------+-----------+------+-----+---------+-------+
| pw_name         | char(32)  | NO   | PRI |         |       |
| pw_passwd       | char(40)  | YES  |     | NULL    |       |
| pw_uid          | int(11)   | YES  |     | NULL    |       |
| pw_gid          | int(11)   | YES  |     | NULL    |       |
| pw_gecos        | char(48)  | YES  |     | NULL    |       |
| pw_dir          | char(160) | YES  |     | NULL    |       |
| pw_shell        | char(20)  | YES  |     | NULL    |       |
| pw_clear_passwd | char(16)  | YES  |     | NULL    |       |
+-----------------+-----------+------+-----+---------+-------+
8 rows in set (0.00 sec)

MariaDB [vpopmail]>



Thank you.

Havrla