The mail server I am pulling e-mail from inserts a "Received" header that looks like the following:
Received: from unknown (HELO host.domain.tld) (192.168.255.254) by ...
BTW - The name "unknown" is always used. I assume they are purposely saving processing power by not reverse-looking up the host name.
I have debugged this problem in the code, and it appears that because the IP address is not surrounded by square brackets, computeRemoteAddress is unable to find the IP address. So the name "unknown" is always used to determine the address instead, which fails.
FYI - The e-mail I am pulling actually passes through two e-mail servers by different organizations, and they both use this format. So I assume this format is common.