Recipient unknown 如何解决！！！急

shenvo

Thu 2004-09-16 10:48:31: [600:3:1] Accepting SMTP connection from [216.136.175.29 : 20674]<br>
Thu 2004-09-16 10:48:31: [600:3:1] Looking up PTR record for 216.136.175.29 (29.175.136.216.IN-ADDR.ARPA)<br>
Thu 2004-09-16 10:48:31: [600:3:1] D=29.175.136.216.IN-ADDR.ARPA TTL=(20) PTR=[web13903.mail.yahoo.com]<br>
Thu 2004-09-16 10:48:31: [600:3:1] Gathering A-records for PTR hosts<br>
Thu 2004-09-16 10:48:32: [600:3:1] D=web13903.mail.yahoo.com TTL=(30) A=[216.136.175.29]<br>
Thu 2004-09-16 10:48:32: [600:3:1] --> 220 mail.sninfo.gov.cn ESMTP MDaemon 6.8.5; Thu, 16 Sep 2004 10:48:32 +0800<br>
Thu 2004-09-16 10:48:32: [600:3:1] <-- HELO web13903.mail.yahoo.com<br>
Thu 2004-09-16 10:48:32: [600:3:1] --> 250 mail.sninfo.gov.cn Hello web13903.mail.yahoo.com, pleased to meet you<br>
Thu 2004-09-16 10:48:32: [600:3:1] <-- MAIL FROM:<shenvo@yahoo.com><br>
Thu 2004-09-16 10:48:32: [600:3:1] --> 250 <shenvo@yahoo.com>, Sender ok<br>
Thu 2004-09-16 10:48:32: [600:3:1] <-- RCPT TO:<liuf@sninfo.gov.cn><br>
Thu 2004-09-16 10:48:32: [600:3:1] Sender attempted to deliver message to unknown address<br>
Thu 2004-09-16 10:48:32: [600:3:1] --> 550 <liuf@sninfo.gov.cn>, Recipient unknown<br>
Thu 2004-09-16 10:48:33: [600:3:1] <-- QUIT<br>
Thu 2004-09-16 10:48:33: [600:3:1] --> 221 See ya in cyberspace<br>
Thu 2004-09-16 10:48:33: [600:3:1] SMTP session successful, 96 bytes transferred.<br>
Thu 2004-09-16 10:48:33: ----------<br>
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最近老是这问题，从哪发来的都提示Recipient unknown，大家帮我看看是怎么了？