今天测试邮箱系统，Telnet方式发信，发了几次都不成功，后来发现原来是我少写了“Subject”这个字段。今天发篇文章提醒自己千万不要再犯这样错误。

下面是正确的步骤：

[root@ws01 root]# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost (127.0.0.1).
Escape character is '^]'.
220 #2172002 Helo Welcome,Naesa Umail-TX v1.6.1 Service ready
ehlo
250-XUSR
250-AUTH LOGIN PLAIN
250 HELP
auth login
334 VXNlcm5hbWU6
amVwaGU=
334 UGFzc3dvcmQ6
bXlwYXNzd29yZA==
235 2.0.0 OK Authenticated
mail from:ymail@163.com
250 #2172005 Ok
rcpt to:ymail@126.com
250 #2172005 Ok
data
354 Start mail input; end with CRLF.CRLF
subject:testing..........
from:
to:
hi,hello!
.
250 #2172005 Ok queue-id: 31
quit
221 #2172003 test GoodBye!
Connection closed by foreign host.
[root@ws01 root]#