With Postfix, the format is: Received: from HELO (FCRDNS [IPADDR]) ...
According to RFC 5321 section 4.4:
This line MUST be structured as follows:
o The FROM clause, which MUST be supplied in an SMTP environment,
SHOULD contain both (1) the name of the source host as presented
in the EHLO command and (2) an address literal containing the IP
address of the source, determined from the TCP connection.
But I did not predict RFC 5321. I simply stole from Sendmail.
Wietse
