dsn=5.1.1, stat=User unknown

I have a linux machine configured to send emails to our vessels, but now they aren't working anymore. I think they aren't accepting messages because our linux machine is not configured as an mx.

Take a look at log file /var/log/maillog
Jul 13 10:02:23 intra sendmail[27973]: p6DD2NA5027973: from=star, size=187307, class=0, nrcpts=1, msgid=<20110713130222.GA27971@intra>, relay=star@localhost
Jul 13 10:02:23 intra sendmail[27974]: p6DD2Na5027974: from=<star@intra.norsul.com>, size=187465, class=0, nrcpts=1, msgid=<20110713130222.GA27971@intra>, proto=ESMTP, daemon=MTA, relay=intra.norsul.com [127.0.0.1]
Jul 13 10:02:23 intra sendmail[27973]: p6DD2NA5027973: to=nstppxc@norsul.amosconnect.com, ctladdr=star (501/501), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=217307, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (p6DD2Na5027974 Message accepted for delivery)
Jul 13 10:02:28 intra sendmail[27976]: p6DD2Na5027974: to=<nstppxc@norsul.amosconnect.com>, ctladdr=<star@intra.norsul.com> (501/501), delay=00:00:05, xdelay=00:00:05, mailer=esmtp, pri=307465, relay=relay1.station12.com. [212.165.122.17], dsn=5.1.1, stat=User unknown
Jul 13 10:02:29 intra sendmail[27976]: p6DD2Na5027974: p6DD2Ta5027976: DSN: User unknown
Jul 13 10:02:29 intra sendmail[27976]: p6DD2Ta5027976: to=<star@intra.norsul.com>, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=218717, dsn=2.0.0, stat=Sent

When I send to my company email (exchange) and to my personnal email (gmail) there is no matter, it only occours when I try to send to the vessels, who is configured to domain norsul.amosconnect.com

Do you have an idea how to solve this problem?