SMTP Service shows Origin IP

Hello.

I am running a VPS as Webserver. It uses PHP Mailer to send emails. I hide the webserver IP behind Cloudflare.

So I figured out I need a SMTP Provider, which I configurated but it still shows the real IP of the webserver in the email header.

I need someone that can help me getting this:

Received: from [127.0.0.1] (localhost [127.0.0.1])

Instead of:

Received: from [webserver IP] (helo=127.0.0.1)

Because if IP leaks this makes Cloudflare useless.