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I am studying the SMTP protocol and follow a course materials to setup a PoC spoofed email by talking with a SMTP server of our department.

This is what I have right now:

shuaiw@shuaicpu1:~$ telnet mail.XXXXXX 25
Trying XXX...
Connected to mail.XXX.hk.
Escape character is '^]'.
220 XXX ESMTP ; Mon, 4 Nov 2019 16:07:07 +0800
HELO random.org
250 XXX Hello 191host060.mobilenet.XXX [XXX], pleased to meet you
MAIL FROM: <test@random.org>
250 2.1.0 <test@random.org>... Sender ok
RCPT TO: <XXX@XXX>                      <---- this is a valid email address
250 2.1.5 <XXX@XXX>... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
this is the email body
.
550 5.7.1 can't determine Purported Responsible Address

I was expecting to send this message out but however, it returns can't determine Purported Responsible Address. Could anyone shed some lights on this? Thanks a lot.

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DATA
354 Enter mail, end with "." on a line by itself
this is the email body
.

You don't send any mail header which also means that you don't send any From field in the mail header which means that server cannot extract From and use it for verification. See also RFC 4407 - Purported Responsible Address in E-Mail Messages.

  • I didn't get that. I do specify a From field, which is at MAIL FROM: <test@random.org>. Am I missed anything here? Thank you! – lllllllllllll Nov 4 '19 at 8:34
  • @lllllllllllll: "I do specify a From field, which is at MAIL FROM: <test@random.org>" - The MAIL FROM command in the SMTP protocol is not the From field in the mail header (which gets send within DATA). Please read RFC 5321 (SMTP) vs. RFC 5322 (Mail) – Steffen Ullrich Nov 4 '19 at 8:45

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