You can hide the client/sender ip and the user agent in the postfix main.cf
Thats the way you do it
nano /etc/postfix/main.cf smtp_header_checks = pcre:/etc/postfix/smtp_header_checks
nano /etc/postfix/smtp_header_checks /^Received:.*with ESMTPSA/ IGNORE
The whole client ip was displayed.
Received: from [192.168.2.231] (XXXXXXX.dip0.t-ipconnect.de [79.XXX.224.XXX]
Just the server ip is displayed.
Received: from pizza.mattionline.de (pizza.mattionline.de. [22.214.171.124])