Update: Starting November 2022, protection.microsoft.com URL does not work anymore. Please go to security.microsoft.com instead for the AntiSpam feature mentioned in this post.
We realize that many...
Updated Dec 08, 2023
Version 10.0
Blog Post
Hi all,
first of all: it's pretty so useful article, compliments The_Exchange_Team !!!
Assuming all of mentioned auto-forward disabling possibilities are in production (from internal to any external domain):
- Outbound spam filter policy: Automatic - System-controlled
- Remote Domains: Default (*) - Allow automatic forwarding disabled
- Mail flow rule: "Client external rules forwarding block control"
- RBAC: option to setup forwarding is hidden
When a user setup an Inbox Rule (Outlook Web) forwarding message from internal's recipient to external, the message is not delivered (due to policy restrictions, of course), however the sender doesn't receive any NDR (so it isn't aware about non-deliverable).
The Message Trace shows a Drop event with description: Reason: [{LED=250 2.1.5 RESOLVER.MSGTYPE.AF; handled AutoForward addressed to external recipient};{MSG=};{FQDN=};{IP=};{LRT=}]
Is this an expected behavior?
Tried to set Outbound spam filter policy to On but it seems the Mail flow rule is not matched.
Note: Due to point 1, NDR is issued to the original sender exclusively in cases where the forwarding is configured via ForwardingAddress or ForwardingSmtpAddress by an Exchange Online administrator (due to point 4).
Any thoughts ?