What is the state of the art with SMTP mail forgeries? It seems that the forwarding SMTP agent can determine the senders IP address. I am wondering if this could be prevented by using IP level spoofing to put fake return IP address on the TCP/IP connection to the receiving mail hubs SMTP port, in that the sender does not really need the information the SMTP hup sends back. This would then be a variant of the IP spoof attack. What would be needed would be a site which blindly accepted the one sided traffic from the receiving SMTP hub where it thought it was replying to the traffic. eg. Sender says: HELO nsa.gov 250 locahost Hello locahost [127.0.0.1], pleased to meet you The sendmail seems to be trying to be clever doing a reverse name lookup, and ignoring what you tell it on the HELO line. The 250 reply is not required by the sender. MAIL FROM: nobody@nsa.gov 250 nobody@nsa.gov... Sender ok RCPT TO: joe@acme.com 250 joe@acme.com... Recipient ok DATA 354 Enter mail, end with "." on a line by itself asdfasdfasdf