My Server has 4 IP addresses.
(IPs are for example only) 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52
Under IIS, I have a Virtual SMTP Server on 184.108.40.206, on port 25. The virtual server installed there at the start on 220.127.116.11 is disabled.
18.104.22.168 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 22.214.171.124 with no reference to 126.96.36.199 at all.