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Exchange hybrid - Users with on-prem mailboxes are being considered 'unauthenticated'
Overview + Setup Information This issue relates to Exchange, SharePoint Online and Office 365. Here's a quick summary of our setup: We've integrated our on-prem AD with Azure AD via Azure AD...
Moreover those messages are sent from the SPO backend, so Exchange is not even involved. Have you tried allowing just the no-reply@sharepointonline.com address?
Adding mailto:no-reply@sharepointonline.com as a mail-enabled contact in AD and Exchange on-prem resolved the issue.
It seems like emails from this address are now being considered 'authenticated' given that they are going through to all distribution group members without my having to disable the 'Require that all senders are authenticated' option for the distribution group in EMC.
Thanks VasilMichev - not sure if this is what you meant, but it gave me the idea anyway.