telnet 的解析

作者: Baron. Wan

telnet localhost 25
example.com.tw ......
HELO gmail.com
MAIL FROM: < yyy @ gmail.com >
RCPT TO: < ggg @ uuu.com.tw >
DATA
from: < yyy @ gmail.com >
to: < ggg @ uuu.com.tw >
subject: test
test
.
QUIT

一封信件的檔頭解析如下:
Received: from gmail.com (localhost.localdomain [127.0.0.1])
by example.com.tw
for ggg @ uuu.com.tw
X-Envelope-From: yyy @ gmail.com
Return-Path: yyy @ gmail.com

那個 `by` 為實際發信的地址