Non-Delivery Report: [550 5.7.350 Remote server returned message detected as spam]

Scenario

You have configured Exclaimer Cloud for your Microsoft 365 tenancy and you notice some messages are rejected with a Non-Delivery Report (NDR), similar to the example shown below:

DSN generated by:  MMXP123MB1230.GBRP123.PROD.OUTLOOK.COM
Remote server:  smtp.eu1.exclaimer.net

Reason

Typically, this scenario occurs if the Mail Routing option in Exclaimer Cloud is configured as Sender Domain. This configuration results in Exclaimer Cloud delivering the message to the server specified on the sending domain name’s MX records.

Resolution

Follow these steps to resolve the issue:

1. Log into the Exclaimer portal (portal.exclaimer.com) and Launch your subscription.
    
2. From the left-hand pane, click Configuration, then select Manage Mail Flow.
    
3. In the right-hand pane, under Mail Routing Domain, are the relevant options.
    
4. In Domain Name, enter the .omnicrosoft.com domain name - this can be located in the Domain list in the Microsoft 365 Admin Center. This setting is important, and an incorrect domain can result in mail flow issues.
   
   Example: 
   
5. Click SAVE to save the changes made.