Remote Server returned '554 5.4.108 SMTPSEND.DNS.MxLoopback

Jeffrey Lagman 0 Reputation points

We are currently settings a new electronic Fax system that will allow us to forward any fax to our emails. But we are getting this error message "Remote Server returned '554 5.4.108 SMTPSEND.DNS.MxLoopback" when doin a test. We have an On-Prem 2016 exchange server.

Exchange Server
Exchange Server
A family of Microsoft client/server messaging and collaboration software.
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  1. Noah Ma-MSFT 2,340 Reputation points Microsoft Vendor

    Hi @Jeffrey Lagman ,

    Thank you for posting to Microsoft Community.

    Based on your description, I understand you got error message "554 5.4.108…” when you test the new electronic Fax system.

    However, I want to confirm that if you are in Exchange Hybrid environment.

    This error can be caused to the mailboxes that don't have the address policy applied, the required remote routing address can't be configured.

    Instead of the correct remote routing address, the default email address of the mailbox may be configured as the remote routing address.

    Therefore, please try to configure the correct remote routing address "" for the mailbox as screenshot below to fix the issue.

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    If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.