Заголовок письма из анализа сервера

Сегодня получил письмо, которое, похоже, пришло из учетной записи из нашего домена, но при анализе заголовка письма оно пришло от другого сервера и пользователя.

Почта пришла с реального домена и была направлена ​​на реальную учетную запись в моем домене.

Как это возможно?

Как я могу избежать этой проблемы?

Заголовок письма отредактирован частично в целях безопасности:

Received: from SN6PR06MB4765.namprd06.prod.outlook.com (2603:10b6:805:ca::39)
 by SN6PR06MB4765.namprd06.prod.outlook.com with HTTPS via
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Received: from BL2NAM02FT029.eop-nam02.prod.protection.outlook.com
 (2a01:111:f400:7e46::204) by DM6PR06CA0047.outlook.office365.com
 (2603:10b6:5:54::24) with Microsoft SMTP Server (version=TLS1_2,
 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1558.16 via Frontend
 Transport; Thu, 24 Jan 2019 17:27:20 +0000
Authentication-Results: spf=pass (sender IP is 66.96.184.5)
 smtp.mailfrom=eigbox.net; **myrealdomain.com**; dkim=none (message not signed)
 header.d=none;**myrealdomain.com**; dmarc=fail action=oreject
 header.from=**myrealdomain.com**;compauth=fail reason=000
Received-SPF: Pass (protection.outlook.com: domain of eigbox.net designates
 66.96.184.5 as permitted sender) receiver=protection.outlook.com;
 client-ip=66.96.184.5; helo=bosmailout05.eigbox.net;
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 Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 15.20.1558.11 via Frontend Transport; Thu, 24 Jan 2019 17:27:20 +0000
Received: from bosmailscan09.eigbox.net ([10.20.15.9])
    by bosmailout05.eigbox.net with esmtp (Exim)
    id 1gmime-0001Df-40
    for **realuserindomain@myrealdomain.com**; Thu, 24 Jan 2019 12:27:20 -0500
Received: from [10.115.3.33] (helo=bosimpout13)
    by bosmailscan09.eigbox.net with esmtp (Exim)
    id 1gmime-00083z-09
    for *realuserindomain@myrealdomain.com**; Thu, 24 Jan 2019 12:27:20 -0500
Received: from bosauthsmtp06.yourhostingaccount.com ([10.20.18.6])
    by bosimpout13 with 
    id UHSH1z00E07rX7u01HSLMQ; Thu, 24 Jan 2019 12:26:20 -0500
X-EN-SP-DIR: OUT
X-EN-SP-SQ: 1
Received: from [190.146.197.219] (port=9098 helo=10.1.29.91)
    by bosauthsmtp06.eigbox.net with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256)
    (Exim)
    id 1gmilb-0004Nx-Pw
    for *realuserindomain@myrealdomain.com**; Thu, 24 Jan 2019 12:26:17 -0500
Date: Thu, 24 Jan 2019 12:26:21 -0500
**From: Presidencia <userinmyrealdomain@myrealdomin.com>**

Заранее спасибо.