Error: Reason: [{LED=454 4.7.5 Remote certificate was not validated}]

Scenario

Email messages sent to Exclaimer Cloud are not being delivered (or delivery is delayed) and the Microsoft 365 message trace shows an error similar to this: 

Reason

Typically, this scenario occurs if the Mail Routing options in Exclaimer Cloud are configured to return messages to the Sender Domain. This configuration tells Exclaimer Cloud to perform a lookup for each processed email, passing the processed email back to the server(s) specified within 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.