Sendmail error 67 user unknown

I think it tries to send email to my domain using VPS server itself, because my VPS server's hostname is my domain name and I see something is running on port 25, is it true?

It should connect to remote SMTP server like what it does for yahoo and aol and msn, and send it to remote smtp server itself, which is hosted in register.com

What do you think?
Thanks from now

It looks like sendmail is running OK if you can send to other addresses, is there a users on that server called 'test' ?

Yes, it's info@mydomain.com and sender is the same. Works well on all domains except my own

Hey, I got a new problem....!!!! NOW sending email to yahoo, aol, hotmail, etc. also not works!!! But I don't get any error

I think I found the problem, look at this:

Apr 11 11:03:40 mydomain sm-mta[23686]: o3BB3egt023686: to=<root@mydomain.com>, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=30000, dsn=2.0.0, stat=Sent
Apr 11 11:06:48 mydomain sendmail[23698]: o3BB6mia023698: from=root, size=298, class=0, nrcpts=1, msgid=<20100411110648.GA23689@mydomain.com>, relay=root@localhost
Apr 11 11:06:49 mydomain sm-mta[23701]: o3BB6mDG023701: from=<root@mydomain.com>, size=452, class=0, nrcpts=1, msgid=<20100411110648.GA23689@mydomain.com>, proto=ESMTP, daemon=MTA-v4, relay=mydomain.net [127.0.0.1]
Apr 11 11:06:49 mydomain sendmail[23698]: o3BB6mia023698: to=someoneexists@gmail.com, ctladdr=root (0/0), delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=30298, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (o3BB6mDG023701 Message accepted for delivery)
Apr 11 11:06:50 mydomain sm-mta[23703]: STARTTLS=client, relay=mail.mydomain.net, version=TLSv1/SSLv3, verify=FAIL, cipher=DHE-RSA-AES256-SHA, bits=256/256
Apr 11 11:06:51 mydomain sm-mta[23703]: o3BB6mDG023701: to=<someoneexists@gmail.com>, ctladdr=<root@mydomain.com> (0/0), delay=00:00:02, xdelay=00:00:02, mailer=relay, pri=120452, relay=mail.mydomain.net [x.x.x.x], dsn=5.1.3, stat=User unknown

It tries to send e-mail from root@mydomain.com

But I want it to send authenticated e-mail from info@mydomain.com and using password I added in /etc/mail/authinfo

If it's using authinfo I added, it should use user: info@mydomain.com and password I defined, if it's not using that, it tries to send and login using user: root@mydomain.com (WHICH DOESN'T EXISTS)

Now could you advice about it?

Thanks

Another update: When I use sendmail with -f paramater, I mean sendmail -f info@mydomain.com

I can send email to yahoo and gmail etc.

But even when I use sendmail -f info@mydomain.com, I can't send email to info@mydomain.com or even anotheremail@mydomain.com

I should authenticate usign info@mydomain.com and password I defined, then I can send email using Register.com's Email Server. But it works on all domains except my own! I think it's because mydomain.com is my VPS server's hostname, is that true? This way sendmail thinks mydomain.com is itself! But how it sends email to yahoo and gmail using mail.mydomain.com (which is hosted in Register.com) ??

Please advice!
Thanks

I syslog I see this:
Apr 11 11:16:33 mydomain sendmail[23749]: o3BBGWWc023749: to=info@mydomain.net, delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=31068, relay=[127.0.0.1] [127.0.0.1], dsn=5.1.1, stat=User unknown
Apr 11 11:16:33 mydomain sm-mta[23750]: o3BBGWvD023750: from=<>, size=1068, class=0, nrcpts=0, proto=ESMTP, daemon=MTA-v4, relay=mydomain.net [127.0.0.1]
Apr 11 11:16:33 mydomain sendmail[23749]: o3BBGWWc023749: o3BBGWWd023749: return to sender: User unknown
Apr 11 11:16:33 mydomain sm-mta[23750]: o3BBGWvF023750: from=<>, size=3659, class=0, nrcpts=1, msgid=<201004111116.o3BBGWWd023749@mydomain.net>, proto=ESMTP, daemon=MTA-v4, relay=mydomain.net [127.0.0.1]
Apr 11 11:16:33 mydomain sendmail[23749]: o3BBGWWd023749: to=postmaster, delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=32092, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (o3BBGWvF023750 Message accepted for delivery)
Apr 11 11:16:33 mydomain sm-mta[23751]: o3BBGWvF023750: to=root, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=33865, dsn=2.0.0, stat=Sent

Seems like it tries to send email to 127.0.0.1, which is wrong and should be mail.mydomain.com hosted in register.com and should also use user/pass I defined

Is it true?

YES! That's true, I see my mail in /var/mail/root

Which should be like that... Any ideas? How to solve it? Please advice