Email delivery / Hybrid Mailflow

Michael Kalu 1 Reputation point
2022-11-08T08:35:26.65+00:00

Email sent from an Exchange online user to a on-premise static DL with all members on Exchange online failed with error “LED=554 5.4.14 Hop count exceeded - possible mail loop” The message trace results show the email first event being “DEFERRED” and then “SEND EXTERNAL” – Why would Exchange online attempt to send the email to the on premise servers in the first place? Was there a mail flow issue with Exchange online between 10:00 - 12:30 today?

The email wasn’t sent to a sub domain and we don’t use Edge servers between the on premise & O365 endpoints.
We are running in Hybrid mode. However, both on premise & Exchange online have the domain “xyz.gov.uk” as authoritative – are you suggesting we should change one or both of these to “Internal relay” ? The majority of our users are still on premise. We are still in the pilot phase. Only IT has been migrated to Exchange online.
The targetAddress of the DL is not set.

Microsoft Identity Manager
Microsoft Identity Manager
A family of Microsoft products that manage a user's digital identity using identity synchronization, certificate management, and user provisioning.
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Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
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  1. Andy David - MVP 140.8K Reputation points MVP
    2022-11-08T12:21:05.39+00:00

    Do you have an outbound connector with an address space of xyz.gov.uk from Exchange Online to on-prem?
    Note DLs do not have a target DL

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  2. KyleXu-MSFT 26,206 Reputation points
    2022-11-09T01:56:12.173+00:00

    @Michael Kalu

    If all members on Exchange online now, I would suggest you delete and recreate this group on Exchange online.

    This group is hosted on Exchange on-premises, just sync to Exchange online, so emails will be sent to Exchange on-premises first.

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