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Copper Contributor

Mar 09, 2018

Undeliverable email messages via Office 365 Exchange

Hi, We have been getting messages that mail delivery has failed. Evidently the error code is 4.4.7. They look like this: ----------------------------------------------------------------------...

MVP

Mar 10, 2018

This is most likely a case of "backscatter" as detailed here: https://blogs.msdn.microsoft.com/tzink/2014/11/22/improving-backscatter-detection-with-boomerang/

Robert Keith
Copper Contributor
Mar 10, 2018
I thought of that. However, all NDR messages are for emails we have actually sent to real recipients, and which have got through. Somehow, Office 365 Exchange is trying to send our legitimate emails to a non-existent address.

Thanks for the suggestion of blocking all NDR messages. It will certainly lower the rate of complaints I am getting about them.

A further mystery is that both affected people use different mail clients. One uses Outlook and I use a Web based service to send and receive.

In any case we are all moving to Zoho mail soon.

Rob
- davidwind
  Copper Contributor
  Oct 14, 2020
  Robert Keith How is ZOHO mail going for you?
- Crimson Castellon
  Copper Contributor
  Mar 10, 2018
  What does message trace in EAC say? If that still doesn't show any clues, it may be time to open a support ticket with Microsoft. Use 'Start-HistoricalSearch' with -MessageTraceDetail parameter to generate a full MTL for them.

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