My Server has 4 IP addresses.
(IPs are for example only) 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168
Under IIS, I have a Virtual SMTP Server on 22.214.171.124, on port 25. The virtual server installed there at the start on 126.96.36.199 is disabled.
188.8.131.52 is mapped to my hostname, mailhost.mydomain.com and the rDNS PTR is configured for that as well.
When I send an Email using mailhost.mydomain.com - it works, but it shows up in headers that the email is coming from 184.108.40.206 with no reference to 220.127.116.11 at all.