Exchange 2003 被中继，如何解决？

xzyshnok

Your message

  To:      kenh@domainname.com.au
  Subject: For: kenh@domainname.com.au
  Sent:    Tue, 21 Apr 2009 17:54:57 +0800

did not reach the following recipient(s):

kenh@domainname.com.au on Tue, 21 Apr 2009 17:55:04 +0800
    The e-mail system was unable to deliver the message, but did not
report a specific reason.  Check the address and try again.  If it still
fails, contact your system administrator.
    < relay03.westnet.com.au #5.0.0 X-Postfix; host
mail.dvjs.com.au[IP Address] said: 550    5.1.1 User unknown (in
reply to RCPT TO command)>

钉子

被中继有几种情况：
1.确实开放了中继。
2.某用户密码被猜出来，进行中继。