Mail sent from a partner's Exchange 2003 to our Exchange 2003 does not pass HELO.
(see the SMTPdiag screen capture from the other server)
Telnet from the other server sends a message successfully.
It's a single instance, mail from other domains is OK.
We have 2 MX records pointing to public IP's from our 2 link providers that are NAT to the Exchange internal address.
There is a link load balancer that handles the 2 ISP's.
I've made a change (after that screen capture) so that both MX records point to the first ISP address but mail still didn't go through.