smtp in IIS7--unable to connect successfully to the destination

I installed SMTP in IIS 7 on windows 2008,and use the default outgoing mail
virtual server in IIS 6 to send mail.
there are two ethernet adapter in the server,one to
internet(,one for cluster.
for the mail virtual server,
properities-->general-->the ip address is,
access-->relay restrictions-->all except the list below
delivery-->outbound security-->anonymous
if telnet 25
send a mail to,it response:
Unable to deliver message to the following recipients, due to being unable
to connect successfully to the destination mail server.


Content-Type: message/delivery-status

Reporting-MTA: dns;
Received-From-MTA: dns;
Arrival-Date: Tue, 30 Dec 2008 00:56:00 -0500

Final-Recipient: rfc822;username@xxxxxxxxxxx
Action: failed
Status: 4.4.7

and when use the smtpdiag,all passed and successfully connect to

and I've closed the firewall in win 2008.

and also nat public ip for the 25 port of

could you help me?
thanks a lot