Issue Postfix E-Mails allways expose sender IP-Address in Authentication-Results header

[hansitheking]

Hello I have already replaced the received headers (IP-REMOVED) which are exposing the client IP-Address of users sending mails from their local clients like explained here: Remove sensitive information from email headers with postfix

But since I am using SPF and DKIM, I have another privacy issue: In every E-Mail the sender IP (93.187.66.176 in my example) is included in the Authentication-Results header. How can I remove this header or the IP-Address in the header.

Received: from [IP-REMOVED] (HOST-REMOVED [IP-REMOVED])
   by server.example.com (Postfix) with ESMTPSA id A1A1666685;
   Thu, 17 May 2018 10:54:48 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=domain.com; s=default;
   t=1526547289; bh=+RRrSiY... tgJUcPY=;
   l=24129; h=From:Subject:To;
   b=nYoHtZg ... bDB0=
Authentication-Results: server.example.com;
        spf=pass (sender IP is 93.187.66.176) smtp.mailfrom=mail@domain.com smtp.helo=macbook.fritz.box

I am using, Ubuntu 16.04.4 LTS‬ with Plesk Onyx, Version 17.8.11 Update #7 with postfix