NDR when sending email to an On-Prem mailbox.

Vijay Kumar 161 Reputation points

I successfully migrated a mailbox from On-Prem to exchange online. It just working fine, mails are receving and able to send as well. However, user had access to an On-prem mailbox which is still at On-prem. When user sending mail to that mailbox address then getting NDR with following description related to distribution group. I don't know why it's saying distribution group and sender and receiver both are mailbox email adddresses. Remote Server returned '550 5.7.133 RESOLVER.RST.SenderNotAuthenticatedForGroup; authentication required; Delivery restriction check failed because the sender was not authenticated when sending to this group'

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Accepted answer
  1. Kael Yao-MSFT 37,586 Reputation points Microsoft Vendor

    Hi @Vijay Kumar,

    Please modify the delivery management setting of the distribution group (which is used to receive the forwarded messages) to allow the original senders (who are using the Send As permission) to send to this group.

    And see if it helps with this issue.

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    1 person found this answer helpful.

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