postfix的問題

[REN]

小弟的POSTFIX,有些信寄不出去,下面是它的錯誤訊息,不知我那裡出錯了?
我的系統是REDHAT LINUX8+POSTFIX

This is the Postfix program at host mail.lbm.com.tw.

I'm sorry to have to inform you that the message returned
below could not be delivered to one or more destinations.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the message returned below.

The Postfix program

<[email protected]>: connect to mx.nyc.untd.com[xx.136.20.83]: server refused
mail service
-------------------------------------------------------------------
Reporting-MTA: dns; mail.lbm.com.tw
Arrival-Date: Fri, 2 May 2003 00:02:24 -0400 (EDT)

Final-Recipient: rfc822; [email protected]
Action: failed
Status: 4.0.0
Diagnostic-Code: X-Postfix; connect to mx.nyc.untd.com[xx.136.20.83]: server
refused mail service