Forum Discussion
Outbound Exchange emails using MX records hitting O365 quarantine if recipient uses O365
Our setup
Incoming: MX record points to O365, which we use solely for spam filtering before sending to on-prem Exchange 2016 using a connector on O365.
Outgoing: Exchange Send Connector set to use MX record of recipient's domain.
Issue
If we send to a recipient that uses O365, these emails are occasionally showing up in our O365 quarantine, flagged by our spoofing prevention mail rule. Looking at the message header, these messages go from our Exchange box to something.mail.protection.outlook.com where they are incorrectly being routed back through our O365 account.
How do I prevent this? I need the spoofing protection, but I can't have O365 blocking outgoing emails.
I'm not sure I completely understand you scenario. You mention the outbound flow is via connector "to the recipient's domain", but then also mention that messages are caught but the O365 outbound spoof rule? Do you perhaps mean that the outbound connector is set to O365 (as in general it should be in such configuration: https://technet.microsoft.com/en-us/library/2e93fd60-a5ef-4e64-8e62-2b862b2d1033(v=exchg.150)#HowdoconnectorsinEOP)?
In general you should consider opening a support case, as this community is not a suitable platform for troubleshooting issues. You can find the support phone numbers here: https://technet.microsoft.com/en-us/library/jj723132(v=exchg.150).aspx
I did end up opening a case.
But no, I made no mistake in my statement. That's why it's so confusing! :(
