This is the official PostfixADM wiki & documentation

Quota service

Create a file called: /etc/xinetd.d/dovecot-quota on your mail server and place the following inside:

service dovecot-quota
        type            = UNLISTED
        port            = 6666
        disable         = no
        socket_type     = stream
        protocol        = tcp
        wait            = no
        user            = vmail
        server          = /usr/local/bin/dovecot-quota
        # configure the IP address(es) of your webserver here:
        only_from      = <YOUR_OTHER_SERVER_IP>
} and exit.

Restart xinetd in order to apply the new service: /etc/init.d/xinetd reload

Now simply test your new service by using telnet: telnet <YOUR_MAILSERVER_IP> 6666 and make sure you can successfully connect.