Authentication-Results - DKIM - change header - email

Question

If I send emails from my server I got the following headers:
Delivered-To: targetemail#gmail.com
Received: by 10.31.231.70 with SMTP id e67csp768117vkh;
Wed, 20 Sep 2017 08:12:10 -0700 (PDT)
X-Google-Smtp-Source: AOwi7QDtqlqxfaVO9FBULHwYV4HU0DKhL6jVf7jUECYVAh8qVNsp+/XIbyzNmIRjoKT0ICWy9Ome
X-Received: by 10.223.169.83 with SMTP id u77mr2134583wrc.268.1505920330877;
Wed, 20 Sep 2017 08:12:10 -0700 (PDT)
ARC-Seal: i=1; a=rsa-sha256; t=1505920330; cv=none;
d=google.com; s=arc-20160816;
b=SIGNATUREHERE
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
h=message-id:content-transfer-encoding:mime-version:subject:to:from
:date:dkim-signature:arc-authentication-results;
bh=+okhXPBeWS3J3wh4Y2Ayn0yURB1edQflYGYjC0IwBQo=;
b=SIGNATUREHERE
ARC-Authentication-Results: i=1; mx.google.com;
dkim=pass header.i=#mydomain.de header.s=default header.b=sQFuh0qx;
spf=pass (google.com: domain of info#mydomain.de designates 123.456.1.1 as permitted sender) smtp.mailfrom=info#mydomain.de;
dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=mydomain.de
Return-Path: <info#mydomain.de>
Received: from mail.mydomain.de (mail.mydomain.de. [123.456.1.1])
by mx.google.com with ESMTPS id k2si1545272wmi.26.2017.09.20.08.12.10
for <targetemail#gmail.com>
(version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
Wed, 20 Sep 2017 08:12:10 -0700 (PDT)
Received-SPF: pass (google.com: domain of info#mydomain.de designates 123.456.1.1 as permitted sender) client-ip=123.456.1.1;
Authentication-Results: mx.google.com;
dkim=pass header.i=#mydomain.de header.s=default header.b=sQFuh0qx;
spf=pass (google.com: domain of info#mydomain.de designates 123.456.1.1 as permitted sender) smtp.mailfrom=info#mydomain.de;
dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=mydomain.de
Received: from mydomain.de (mydomain.de [IPv6:2a01:4f8:10b:1f55::2]) by mail.mydomain.de (Postfix) with ESMTPSA id 1CC703C00E6 for <targetemail#gmail.com>; Wed, 20 Sep 2017 17:12:10 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mydomain.de; s=default; t=1505920330; bh=+okhXPBeWS3J3wh4Y2Ayn0yURB1edQflYGYjC0IwBQo=; l=26446; h=From:To:Subject; b=sQFuh0qxf1rc0fFKeuhDeLoAaacLaFRyCyMw8rMJh80AZFLyLcCpVqKq1nWBBlEE0
1ii+p3Hf9HNqTvSqU66EUIZ0QtIs8GCLJI3m95DN8DpqXFvLFfiK88413zKnufODOS
aodq8Mxq53+6wG/GOmoe5jQMxG5NH1mV720xVlIw=
Authentication-Results: zeus.mydomain.de;
spf=pass (sender IP is 2a01:4f8:10b:1f55::2) smtp.mailfrom=info#mydomain.de smtp.helo=mydomain.de
Received-SPF: pass (connection is authenticated)
Date: Wed, 20 Sep 2017 17:12:10 +0200
From: info#mydomain.de
To: targetemail#gmail.com
Subject: My Subject
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
Content-Transfer-Encoding: quoted-printable
Message-Id: <20170920151210.1CC703C00E6#mail.mydomain.de>
Everything is fine except the following header:
Authentication-Results: zeus.mydomain.de;
How do I have to change my server settings to get that header look like:
Authentication-Results: mydomain.de;
or
Authentication-Results: mail.mydomain.de;
Do I have to change the hostname accordingly, which is zeus.mydomain.de at the moment? Can I achieve the desired header without changing the hostname of the server?

Answer 1

SPF and DKIM matter in this regard only with alignment with your friendly from domain - mydomain.de. If you have domains or subdomains you don't send email "from" you'd still want to do email auth as bad guys can spoof domains and sub-domains that aren't used by you as the from domain in email.