Unable to change to elastic IP

Installed Poste.io pro version. The system keeps recognizing the server IP as the one they provided instead of Elastic IP that I configured it with.

I logged in via Elastic IP and installed the software but keeps going back to default server IP. How do I change this so it recognises and sends emails only through Elastic IP and configures things with Elastic IP as opposed to the server IP they provide for all cloud instances.

It doesn't do that.