Create a file called:
/etc/xinetd.d/dovecot-quota on your mail server and place the following inside:
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 = 127.0.0.1 <YOUR_OTHER_SERVER_IP>
..save and exit.
Restart xinetd in order to apply the new service:
Now simply test your new service by using telnet:
telnet <YOUR_MAILSERVER_IP> 6666 and make sure you can successfully connect.