I use a Strato vServer, with Plesk and Postfix as a Mailserver. My problem is that whenever I send a mail to a Gmail receiver address, the email is received in spam folder. I have tried to set the Reverse DNS address to be the host address of the server, as well as including a IPV6 address, but still the problem continous.
Can anybody tell me how to fix that? Any help is very appreciated.
Here is the Mail Header received by Gmail (which is detected as Spam):
Delivered-To: danielresch888@gmail.com
Received: by 2002:a5b:586:0:0:0:0:0 with SMTP id l6csp3841328ybp;
Tue, 3 Mar 2020 09:26:15 -0800 (PST)
X-Google-Smtp-Source: ADFU+vudlUySOa0Mu2/iOVx5nlYJcJ2HA7CIT0SBh7SnOWB/9e2d1Nu6xtctXWRKM92liX2cwLYJ
X-Received: by 2002:aa7:de8d:: with SMTP id j13mr5129247edv.80.1583256375696;
Tue, 03 Mar 2020 09:26:15 -0800 (PST)
ARC-Seal: i=1; a=rsa-sha256; t=1583256375; cv=none;
d=google.com; s=arc-20160816;
b=bQ79pu2joXUPR+chjwibOSpEFPhZ36uuScUq2hqMs8mGMIWXmayzMN7/iBr7qUYS6C
K634cmjNXkS4+Yy0QH7QhDFhLLHR4oUFF7k7oGrWL2ZSfWMjUFkI90uqcegglBXzo0sh
Eva6rCB3WejVbnftLe+4WdAly0hKwRc89OFKXpQmL1BOQjw7IsJTXTlLKZC2st5/7Iww
F6o7ohZNQLe7inQhY0Vdpo7BA9Eswo5+L7lCILULasn9ko+3+p6B+enrBUIA7BguXsw+
9dcc93ADgnXcsh54NGcbacOqMStSyjIe3QsJUwFgU7cGWRRjQ9QobrGc9qFttEAPYOm4
XleQ==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816;
h=content-disposition:mime-version:user-agent:subject:to:from
:message-id:date;
bh=corQzZ5psnUYHxp2UWTs/GfeRdb+RY0x3zTysuTn8zg=;
b=oAkoSvFIImUqWbyIQ7YjO7WmOgw6PIKKZoNTSFguNZxdlD4Iv37/SSlFi8f2hcgsYc
4CJU0K67l1SHFKHuilEtWNgsq/Ng4rLiL3KZ5U13ZPtUIVNGJc7sBhH0p2cNJlGFIB4P
0YBq5r+q0V+ImO3gYa/f5rMMXzDVCaiYqZME7/SGmrXdoeLjZ/bS/wwJNyUUH2mkkU9S
ML+MgP9IhI5BQ9hLSg87WrXwsxxMFy/D3zSde6U3AZ7UsRyVDZBSYG1Z9b6OW6Ma+BkC
pqVUf6XJax7GwM9v1WqiG4uX7GBrnci9rS8D4gOZd3THSCv/N5fZGd+xt6pN3PpPqZ8I
TSiQ==
ARC-Authentication-Results: i=1; mx.google.com;
spf=pass (google.com: best guess record for domain of office@viewport-design.de designates
81.169.195.81 as permitted sender) smtp.mailfrom=office@viewport-design.de
Return-Path: <office@viewport-design.de>
Received: from viewport-design.de (www.viewport-design.de. [81.169.195.81])
by mx.google.com with ESMTPS id u6si1853224ejr.511.2020.03.03.09.26.15
for <danielresch888@gmail.com>
(version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);
Tue, 03 Mar 2020 09:26:15 -0800 (PST)
Received-SPF: pass (google.com: best guess record for domain of office@viewport-design.de designates
81.169.195.81 as permitted sender) client-ip=81.169.195.81;
Authentication-Results: mx.google.com;
spf=pass (google.com: best guess record for domain of office@viewport-design.de designates
81.169.195.81 as permitted sender) smtp.mailfrom=office@viewport-design.de
Received: from h2820428.stratoserver.net (localhost [IPv6:::1]) by h2820428.stratoserver.net
(Postfix) with ESMTPSA id 2907F2249A for <danielresch888@gmail.com>; Tue,
3 Mar 2020 18:26:15 +0100 (CET)
Received: from 91.141.3.237.wireless.dyn.drei.com (91.141.3.237.wireless.dyn.drei.com [91.141.3.237])
by webmail.viewport-design.de (Horde Framework) with HTTPS; Tue, 03 Mar 2020 17:26:15 +0000
Date: Tue, 03 Mar 2020 17:26:14 +0000
Message-ID: <20200303172614.Horde.vnh6uq7p6LQ6p9XK47vMGnk@webmail.viewport-design.de>
From: office@viewport-design.de
To: danielresch888@gmail.com
Subject: Test Email
User-Agent: Horde Application Framework 5
Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes
MIME-Version: 1.0
Content-Disposition: inline
Test Email