Hydrid DL and 5.4.12 error

Question

In a hybrid exchange environment I deploy a DL on exchange on line. The members of this dl are all on cloud.
If I send an email to dl from inside the organization it works.
If I send an email to dl from outside the organization after some time I recive a messager form postamaster of my organization with error 5.4.12.
The dl deployed onprem works.

Answer 1

@sim3vi

To narrow down this one, I would confirm some information with you:

Whether this phenomenon occurs on all Exchange online distribution group? If this phenomenon only occurs on a specific distribution group. I would suggest you try to create a new one.

Whether you modify the default hybrid connector before? If you modify it before, I would suggest you try to rerun HCW to create a new one.

Which email address that you used for this distribution group? I would suggest you try to use the Exchange online default domain for this group then check whether the phenomenon is gone.

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Answer 2

For the DL to accept messages from outside the organization, you need to remove the requirement that senders need to be authenticated, e.g.
Set-DistributionGroup -Identity <DG ID> -RequireSenderAuthenticationEnabled $False

Note that this may open up the DG for spammers from outside.

Answer 3

You can check these threads for help - https://answers.microsoft.com/en-us/msoffice/forum/all/554-5412-smtp-hop-count-exceeded-possible-mail/cf6fcc51-498b-408b-8552-02e24ef563d6

https://social.technet.microsoft.com/Forums/en-US/c2ee6d84-7026-4421-a885-f1c854718619/554-5412-smtp-hop-count-exceeded-after-editing-user-settings?forum=Exch2016Adm