At 10:17 26-01-2009, Jeff Macdonald wrote:
Doesn't the above also allow the NAT IP as well?
Answering questions involving NAT or SLUT66  is tricky as there
may not be any right answer.
There isn't any mention in RFC 5321 about whether IPv4 addresses
excludes the ranges of IP addresses defined in RFC 1918. I cannot
find a reason to add that to the specifications as SMTP is not
restricted to the Internet or public routable IP addresses only.
Some people may argue that the SMTP client cannot be identified if it
uses a RFC 1918 IP address in an address literal to communicate with
a SMTP server on the Internet. For operational reasons, it's better
for such hosts to relay through a smarthost using SUBMIT.