sendmail 寄信问题. 在线等! 帮忙啊兄弟们!!!

ken

----- The following addresses had permanent fatal errors -----
<user@domin.com>
    (reason: 550-Verification failed for <myuser@mydomin.com>)

   ----- Transcript of session follows -----
... while talking to mail.domin.com.:
>>> DATA
<<< 550-Verification failed for <myuser@mydomin.com>
<<< 550-Unrouteable address
<<< 550 Sender verify failed
550 5.1.1 <user@domin.com>... User unknown
<<< 503 valid RCPT command must precede DATA

请各位兄弟们帮忙看看.很奇怪,有时可以有时不行.发去163.com的就可以.21cn.com的就一时可以一时不行.在线等.再搞不好老板要%^&&*%^#$人啦.