Sometimes the support guys give me a heads up when they write new articles for Microsoft Support. Here are a couple regarding Exchange and Exchange Online Protection, which are in my wheelhouse, so I thought I would re-post them here:
"Relay Access Denied" NDR when you try to send mail flow from an on-premises Exchange organization through Exchange Online Protection - Assume that you try to establish mail flow from an on-premises Microsoft Exchange organization through Microsoft Exchange Online Protection (EOP). However, when you try to send an email message from an on-premises Exchange mailbox to an external recipient, the message is not sent. Additionally, you receive the following non-delivery report (NDR): #550 5.4.1 Relay Access Denied ##
(We also have a topic on TechNet that shows you how to set up your connectors at Set Up Mail Flow Through Exchange Online Protection.)
How to troubleshoot data loss prevention policy tips in Exchange Online Protection in Office 365 - PROBLEM Assume that you create or change a data loss prevention (DLP) policy in Microsoft Exchange Online Protection in Office 365 policy. This policy notifies users when an email message that they create in Microsoft Outlook 2013 contains sensitive information. However, when a user creates an email message that contains sensitive information, the policy tips aren't displayed as expected.