a friend of mine is running a contact form on a website which sends the e-mails through the PHP mail() function (CMS used is Contao). The e-mails are sent without a problem to other recipients, so neither the CMS itself or the server responsible for sending are the problem. However, the two e-mails that these messages are actually supposed to be sent to, are run through Exchange Online (Office 365). It seems like there is some kind of protection going on that blocks these e-mails. Every other e-mail from actual mail clients goes through. I couldn't find any setting in the Exchange AC regarding to this.
Here are the email headers from the contact form messages (sent a message from the contact form to another e-mail, where, again, it is received just fine):
Return-Path: <firstname.lastname@example.org> Delivered-To: email@example.com Received: from premium31.web-hosting.com by premium31.web-hosting.com with LMTP id UBwiOpOw0VsKMAwAmYe65g for <firstname.lastname@example.org>; Thu, 25 Oct 2018 08:01:23 -0400 Return-path: <email@example.com> Envelope-to: firstname.lastname@example.org Delivery-date: Thu, 25 Oct 2018 08:01:23 -0400 Received: from u230.lrnc.net ([220.127.116.11]:47206) by premium31.web-hosting.com with esmtp (Exim 4.91) (envelope-from <email@example.com>) id 1gFeKJ-003PuQ-PW for firstname.lastname@example.org; Thu, 25 Oct 2018 08:01:23 -0400 Received: by u230.lrnc.net (Postfix, from userid 10020) id 15D73C46B8; Thu, 25 Oct 2018 14:01:03 +0200 (CEST) To: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Nachricht =?utf-8?Q?=C3=BCber?= die Webseite Message-ID: <email@example.com> Date: Thu, 25 Oct 2018 12:01:02 +0000 From: firstname.lastname@example.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Priority: 3 (Normal) X-Mailer: Contao Open Source CMS
Could anyone point me to where the problem might be?