sendmail问题

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我已配完了dns,
mx 为mail.linux.com
用nslookup看没有问题
在sendmail.mc 中仅把
dnl DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea')dnl
改为：
DAEMON_OPTIONS(`Port=25, Name=MSA, M=Ea')dnl
然后
m4 /etc/mail/sendmail.mc >; /etc/mail/sendmail.cf
最后把/etc/mail/sendmail.cf
Cwlocalhost
改为
Cwlinux.com

[root@localhost mail]# service sendmail restart
关闭 sendmail：  确定  ]
关闭 sm-client：  确定  ]
启动 sendmail：  确定  ]
启动 sm-client：  确定  ]
[root@localhost mail]# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 localhost.localdomain ESMTP Sendmail 8.12.8/8.12.8; Thu, 27 May 2004 16:35:5
3 +0800
mail from:aa@linux.com
530 5.7.0 Authentication required

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以上为我配置sendmail过程
测试时：530 5.7.0 Authentication required
我不知什么意思？？？
请帮忙！！！