Issue Why do I receive mails from unresolveable domains?

[Azurel]

Plesk Onyx Version 17.8.11 Update #67 (CentOS Linux 7.6.1810)

#1
I get mails from unresolveable domains. Should this not be blocked, as default?

Received: from [223.226.99.*] (unknown [223.226.99.*])

#2
Tools & Settings -> Server-Wide Mail Settings is enabled for "DKIM spam protection":
[yes] Allow signing outgoing mail
[yes] Verify incoming mail
So why I get a faked mail from my own mail-adress? Mail-Header said "dkim=pass".

#3
In DNS Setting of my domain is still this entry

TXT v=spf1 +a +mx -all

But under "Tools & Settings" -> "Server-Wide Mail Settings" -> "SPF spam protection" -> "Enable SPF spam protection to check incoming mail" the checkbox is not checked anymore.


Installed mail server: Postfix
Installed IMAP/POP3 server: Courier-IMAP

 

[AYamshanov]

Hi Azurel,

Could you please post all headers of the email?

 

[Azurel]

The Header was

Authentication-Results: mail;
dkim=pass header.d=example.com
Return-Path: <[email protected]>
X-Original-To: [email protected]
Delivered-To: [email protected]
Received: from [223.226.99.*] (unknown [223.226.99.*])
by mail.testserver.com (Postfix) with ESMTP id 5FB.....D6
for <[email protected]>; Mon, 9 Sep 2019 02:34:02 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=default; t=1567989242;
bh=L2u.....9so=; l=2113;
h=From:To:Subject;
b=vZE.....WNM=
Message-ID: <[email protected]>
From: <[email protected]>
To: <[email protected]>
Subject: Your account is being used by another person!
Date: 9 Sep 2019 09:54:55 +0400
MIME-Version: 1.0
Content-Type: text/plain;
charset="windows-1250"
Content-Transfer-Encoding: 8bit
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2900.5931
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5931

I have now activated SPF (again). I don't know why SPF protection was unchecked.