Linux中使用telnet方式发送邮件

偶然发现我的linux也安装了postfix。用telnet发送邮件非常简单，如下：
# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 cnc-mx.hzqbbc.com ESMTP Postfix - by extmail.org
helo localhost
250 cnc-mx.hzqbbc.com
mail from:<test@extmail.org>
250 2.1.0 Ok
rcpt to:chifeng@extmail.org
250 2.1.5 Ok
Data
354 End data with .
Subject:test
from localhost
.
250 2.0.0 Ok: queued as 70A1D156C4
quit
221 2.0.0 Bye
Connection closed by foreign host.