I'm trying to setup an email server so it has the capability to send email from multiple IP addresses, so our marketing system can send email from multiple domains, while keeping the reverse DNS lookups consistent. IE, domain1.com resolves to 10.0.0.1, domain2.com resolves to 10.0.0.2, etc.
Ideally, the mail server would check the
from domain in the headers, then choose the correct IP address from a pool, using that for the actual sending. Right now, we're using Exim, and I was thinking that one solution would be to run multiple instances of Exim on different interfaces, then write an SMTP proxy that would do the header checking and forward the email to the correct Exim instance, but I'm thinking there may be a simpler solution than that.
Just so everyone knows, this doesn't involve spamming, and we own all the domains and IP addresses we would be using.