Remote Server returned '554 5.4.108 SMTPSEND.DNS.MxLoopback

Jeffrey Lagman 0

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.

1 answer

Noah Ma-MSFT 2,725 Reputation points Microsoft Vendor

2024-06-26T06:10:03.0533333+00:00

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 " mail.onmicrosoft.com" for the mailbox as screenshot below to fix the issue.

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.
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Jeffrey Lagman 0 Reputation points

2024-06-26T06:15:44.5166667+00:00

Hi Noah,

We are not using hybrid setup. Our exchange servers are On-Prem.

Noah Ma-MSFT 2,725 Reputation points Microsoft Vendor

2024-06-28T09:57:01.9266667+00:00

Hi,

To help you better, I would like to confirm with you whether it is sent to internal or external recipients.

If the email sent from a mailbox, such as Outlook or OWA, to the same recipient can also delivered successfully?

Also, please double check if there is the Edge server or receive connector to receive emails generated by Fax sys?

You could refer to Mysterious mail loop on Edge Transport server: Check your size limits! - Microsoft Community Hub for more information.

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.

Jeffrey Lagman 0 Reputation points

2024-06-28T11:05:40.6766667+00:00

Hi Noah,

The email is sent internally, The Fax System should be the one sending the email, but we did a test with Outlook with the same result.

We do not have an Edge server and we already have a receive connector, do we need a new receive connector just for the Fax System

Noah Ma-MSFT 2,725 Reputation points Microsoft Vendor

2024-07-02T09:44:24.84+00:00

Hi,

As you mentioned, I suggest you could try to create a new internal connector that forced messages e-mail internal domains to be processed by Exchange without performing a DNS lookup to see if it works.

Hope it helps.
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Remote Server returned '554 5.4.108 SMTPSEND.DNS.MxLoopback

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