发到某些邮箱时，出现451 : mailbox unavailable

一对一

03:13 14:02 SMTP-(c378018100000613) Connect dns.com.cn [122.70.138.30:25] (1)
03:13 14:02 SMTP-(c378018100000613) 220 mailmx.dns.com.cn ESMTP Mirapoint Messaging Server MOS 3.8.3-GA Queueing
03:13 14:02 SMTP-(c378018100000613) >EHLO xxx
03:13 14:02 SMTP-(c378018100000613) 250-mailmx.dns.com.cn Hello yvsy
03:13 14:02 SMTP-(c378018100000613) 250-8BITMIME
03:13 14:02 SMTP-(c378018100000613) 250-SIZE 15728640
03:13 14:02 SMTP-(c378018100000613) 250-ETRN
03:13 14:02 SMTP-(c378018100000613) 250-DSN
03:13 14:02 SMTP-(c378018100000613) 250-AUTH LOGIN
03:13 14:02 SMTP-(c378018100000613) 250-AUTH=LOGIN
03:13 14:02 SMTP-(c378018100000613) 250 PIPELINING
03:13 14:02 SMTP-(c378018100000613) >MAIL FROM:<xxx@xxx.com>
03:13 14:02 SMTP-(c378018100000613) 250 Sender OK
03:13 14:02 SMTP-(c378018100000613) >RCPT To:<yxxx@dns.com.cn>
03:13 14:02 SMTP-(c378018100000613) 451 Requested mail action not taken: mailbox unavailable
03:13 14:02 SMTP-(c378018100000613) >QUIT
03:13 14:02 SMTP-(c378018100000613) 221 mailmx.dns.com.cn Goodbye


这是什么原因，是我这边哪没设置好？

ineedrmb

应该是对方服务器的问题。