We have received consistent feedback from our customers that the ability to reject messages for invalid recipients at the service network perimeter is important. We are aggressively working to desi...
Updated Jul 01, 2019
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Blog Post
Hi Don - if you have an environment which is shared across Exchange Online and an on-premises mailbox infrastructure you will still have the ability to have the recipient rejection performed within the service even after the upgrade to wave15. This is why DBEB is not an upgrade blocker for customers unless they are FOPE Standalone (no Exchange Online integration at all). As I mentioned earlier, when an Exchange Online customer has added all of their valid recipients to the Office 365 Active Directory you can change your domain type to "Authoritative" in the service. "Authoritative" means that all known recipients are discoverable, and if the recipient doesn't exist then the messages are rejected. It does not matter whether initial delivery of your mail is destined for an on-premises environment or routed through the cloud initially. If the recipient is in the directory, the mail will be accepted. Customers today who have no Exchange Online integration (who are being upgraded to EOP Standalone) do not have the ability to configure their domain type in Office 365. Without that ability today, they cannot perform recipient validation within the service. You can, however. I really hope that helps.