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