mail to another machine on the LAN

[Hiisi]

ke, 2010-10-27 kello 19:03 +0800, Ed Greshko kirjoitti:
> 
> First, you haven't said what router you are using.  While it sounds as
> if you will have to set up a local name server to properly resolve the
> hostname of 192.168.3.30 to its IP address you may want to consult the
> router's documentation and/or contact the manufacturer of the router.
> 
> FWIW, I am assuming the error you reported is being seen in the logs of
> the router.
> 

No, the router is my F12 computer that is connected to the Internet and
shares its connection with LAN machines. Sorry if it wasn't too clear.
Should I call it the gateway?
Yes, there's an error in /var/log/maillog on the gateway:
Oct 27 14:55:18 kello sendmail[9440]: o9RAtHE6009440:
to=user@[192.168.3.30], ctladdr=root (0/0), delay=00:00:01,
xdelay=00:00:00, mailer=relay, pri=30214, relay=[127.0.0.1] [127.0.0.1],
dsn=2.0.0, stat=Sent (o9RAtIZj009442 Message accepted for delivery)
Oct 27 14:55:18 kello sendmail[9444]: o9RAtIZj009442:
to=<user@[192.168.3.30]>, ctladdr=<root at kello.ru> (0/0), delay=00:00:00,
xdelay=00:00:00, mailer=esmtp, pri=120435, relay=[192.168.3.30]
[192.168.3.30], dsn=5.7.1, stat=User unknown
Oct 27 14:55:18 kello sendmail[9444]: o9RAtIZj009442: o9RAtIZj009444:
DSN: User unknown

It is the only mention of it in the maillog. If I send messages to
user at 192.168.3.30 (without brackets around addr) then there's nothing in
log files and the message is returned to sender with reason: 550 Host
unknown.
-- 
A chronic disposition to inquiry deprives domestic felines of vital qualities.