On my Windows server 2008, I have IIS 7, ColdFusion 9, and the virtual SMTP service installed.
I host several applications on the server that send emails using the virtual SMTP service. Each application has its own separate SMTP virtual server so that the FQDN in the email header will match the email from address. Each application also has its own public IP address and the SMTP server acts on different public IP addresses.
I have configured RDNS lookups for those IP addesses that match the FQDN, which should make email recipient happy.
However, to the email recipient hosts, those IP addresses are not actually the ones connecting; instead the recipient hosts see the WAN IP address of the router. Many of the mail recipients are rejecting our email because a RDNS lookup on that IP address fails. Simply adding a RDNS lookup for that address would not be a total solution, because we need distinct IP addresses for the different domain names on the machine.
How can I resolve this so that my email headers show the public IP address of the SMTP server and not the router?