On Fri, Feb 3, 2012 at 8:14 AM, Reindl Harald h.reindl@thelounge.net wrote:

on both sides of the NAt you need a DNS with the correct mapping the host on the other side is not interested in your NAT it sees a IP, a HELO and DNS-Records

so it is YOUR job as admin to provide the correct HELO for your outgoing IP and even configure the DNS behind the NAT correctly if you like it really clean

Your HELO has nothing to do with your source IP, and you can't possibly expect a multi-homed server to adjust its HELO to the interface it happens across. Expecting the reverse DNS of the source IP to give a name that has the same IP in an A record lookup is somewhat different, but still I don't think that is an actual requirement. As a mail admin, you are of course free to discard your users' mail for any whimsical reason you like, but if you want to say it is a requirement, please quote the MUST in an RFC.