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<p>In this case, the email messages are delivered correctly into the
Office365 network for domains hosted by Office365.<br>
(Our logs show the outlook.com MX records accepting delivery)<br>
The problem is happening internal to their network, where a rogue
mail flow rule for one customer is rerouting all emails from one
of our servers.</p>
<p>It appears Office365 customers are allowed to add IP address
based rules (in particular "mail flow connectors") without
authentication which could be used by a malicious office365<br>
user to effectively divert all mail from a source IP regardless of
recipient into their account. <br>
<br>
I am still in the process of trying to escalate within the
Office365 support channels, but not having much luck so far...<br>
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<div class="moz-cite-prefix">On 22/05/2019 11:54 am, Paul Wilkins
wrote:<br>
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<blockquote type="cite"
cite="mid:CAMmROT+t6U3V0Nm-BDuorNWB08-SuYifL86y+YDhXnJErSsCOw@mail.gmail.com">
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<div>Martin,</div>
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<div>Just so we're all on the same page, email routing is never
directly related to IP allocations, it's MX bound if properly
standards compliant. And if the canonical MX record is
directing to the alternate customer, the problem lies with DNS
not email.</div>
<br>
Kind regards<br>
<br>
Paul Wilkins<br>
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