How HOTMAIL authenticate received messages?

Does anyone know which mechanism does HOTMAIL use to authenticate received emails? Recently I received in my inbox a spam from snipped-for-privacy@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

************************************************ 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
formatting link
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: snipped-for-privacy@viff.org

250 snipped-for-privacy@viff.org....Sender OK

RCPT TO: my snipped-for-privacy@hotmail.com

250 my snipped-for-privacy@hotmail.com

DATA

354 Start mail input; end with . From: To: Subject: SMTP test

SMTP test body

. 250 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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Andre
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