Change headers in postfix

Hi all,

I need help with the configuration in my vps. I am using the postfix software to send the email and when I send the email from my server using PHP, I can see the local host in the header that looks like this:

Code:

Received: from localhost (gateway1.mydomain.com [104.xxx.xxx.xx]) by mail.mydomain.com (Postfix) with ESMTPSA id E118F7B89DCD for ; Mon, November 26, 2018 14:49:35 -0500 (EST)

I want to delete it and replace it with my domain name so that my email is displayed as authentic.

Do you know how I can delete the local host to replace it with my domain name?

Any advice would be much appreciated.

Thanks in advance.