How HOTMAIL authenticate received messages?

[Andre]

Does anyone know which mechanism does HOTMAIL use to authenticate
received emails?
Recently I received in my inbox a spam from v...@viff.org. And tried
to reproduce it by sending the following SMTP message to HOTMAIL, but
although HOTMAIL queued for delivery, it never showed up in my inbox.
Could HOTMAIL be comparing the IP address of the sender with the
address returned by a DNS query for the mail server of the sender's
domain (nslookup -querytype=mx viff@org) stated in the EHLO header to
authenticate these messages? In this case a spam sent from the
viff.org email server would go through. While another spam send from
another domain, but claiming to come from viff.org would be blocked?
If so, is there any documentation on the net about it?

Thanks in advance,

Andre

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andre@kirchner:~$ telnet mx4.hotmail.com 25
Trying 65.54.244.232...
Connected to mx4.hotmail.com.
Escape character is '^]'.
220 bay0-mc7-f2.bay0.hotmail.com Sending unsolicited commercial or
bulk e-mail to Microsoft's computer network is prohibited. Other
restrictions are found at http://privacy.msn.com/Anti-spam/.
Violations will result in use of equipment located in California and
other states. Sat, 2 Feb 2008 12:16:29 -0800

EHLO testing.com
250-bay0-mc7-f2.bay0.hotmail.com (3.5.0.22) Hello [76.77.66.100]
250-SIZE 29696000
250-PIPELINING
250-8bitmime
250-BINARYMIME
250-CHUNKING
250-AUTH LOGIN
250-AUTH=LOGIN
250 OK

MAIL FROM: v...@viff.org
250 v...@viff.org....Sender OK

RCPT TO: my_em...@hotmail.com
250 my_em...@hotmail.com

DATA
354 Start mail input; end with <CRLF>.<CRLF>
From: <v...@viff.org>
To: <my_em...@hotmail.com>
Subject: SMTP test

SMTP test body

..
250 <BAY0-MC7-F2kzYDGj9C000b5...@bay0-mc7-f2.bay0.hotmail.com> Queued
mail for delivery

QUIT
221 bay0-mc7-f2.bay0.hotmail.com Service closing transmission channel
Connection closed by foreign host.

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