Login and send email as 127.0.0.1

I have this problem:

Code:

2013-01-21 19:40:28 1TxMIG-0001vd-J7 <= newcasino@domain.com H=localhost (Unknown) [127.0.0.1]:42586 I=[127.0.0.1]:25 P=smtp S=7105 id=64ABD65002A149DEAFE3CB79F017F$
2013-01-21 19:40:28 SMTP connection from localhost (Unknown) [127.0.0.1]:42586 I=[127.0.0.1]:25 closed by QUIT
2013-01-21 19:40:28 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1TxMIG-0001vd-J7
2013-01-21 19:40:28 1TxMIG-0001vd-J7 SMTP connection identification H=localhost A=127.0.0.1 P=42586 M=1TxMIG-0001vd-J7 U=root ID=0 S=root B=authenticated_local_user
2013-01-21 19:40:28 1TxMIG-0001vd-J7 ** atay@otherdomain.com F=<newcasino@domain.com> R=fail_remote_domains: The mail server could not deliver mail to atay@otherdomain.$
2013-01-21 19:40:28 cwd=/var/spool/exim 7 args: /usr/sbin/exim -t -oem -oi -f <> -E1TxMIG-0001vd-J7
2013-01-21 19:40:28 1TxMIG-0001vp-ST <= <> R=1TxMIG-0001vd-J7 U=mailnull P=local S=8067 T="Mail delivery failed: returning message to sender" from <> for newcasino@dom$
2013-01-21 19:40:28 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1TxMIG-0001vp-ST
2013-01-21 19:40:29 1TxMIG-0001vd-J7 Completed

I tried to fix it, but did not succeed.
Any suggestion to block this situation?
thanks.