Non-Delivery Report: [550 5.4.1 Recipient address rejected: Access denied]

If an incorrect routing address is in the Exclaimer Settings

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. 
   
   
   NOTES: The MX record for the Domain name (in the Mail Routing settings) should specify a single Exchange Online Server for your Microsoft 365 tenancy. 
   
   - To check the MX record for your own Domain name, use a DNS lookup tool, such as MXToolbox. 
   
   Example showing Exclaimer's domain:
   

Force the replication of the connectors within the Microsoft 365 environment

1. Delete the Exclaimer transport rule.
   
   -Log in to the Exchange admin center using your Microsoft 365 Administrator credentials.
   
   - Select mail flow from the left-hand pane, then select rules.
   
   - You will see the Transport Rule you created when setting up Signatures for Office 365.
   
   - Click the trashcan icon above the Transport Rule.
   
   
   A Warning message is displayed, prompting you to confirm if you want to permanently delete the Transport Rule.
   
   -Click Yes to permanently delete the Transport Rule.
   
   WARNING! Once the Transport Rule has been deleted, it cannot be undone.
2. Delete both Exclaimer connectors.
   
   -Highlight the Receive connector and click the trashcan icon:
   
   A Warning message is displayed, prompting you to confirm if you want to delete the selected connector.
   
   - Click Yes to permanently delete the selected connector.
   WARNING! Once the Office 365 connectors are deleted, they cannot be undone.
   
   - Repeat the same process to delete the Send connector.
   
   - With the Transport Rule and Office 365 connectors deactivated/deleted, your emails will no longer be routed to an Exclaimer Azure server, and signatures will not be added to any emails.
   
   
3. Remove the Exclaimer domain:
   - In the Microsoft 365 Admin Center, navigate to Settings > Domains (via the left-hand navigation pane).
   
   - On the Domains page, select the required domain (this will be in the form <unique tenant ID>.smtp.exclaimer.cloud).
   
   - Click Remove.
   
   - Follow any additional prompts, then click Close.
   
   For additional information, see how you can remove the Exclaimer domain.
   
   
4. Re-run the connector setup.

If your public folders are hosted on-premise

1. Open the Microsoft Azure Active Directory Connect screen.
   
   
2. Select  Optional Features on the left-pane, then tick Exchange Mail Public Folders on the right-pane.
   
    

This will ensure that Mail Enabled Public Folders addresses will no longer be considered invalid addresses by DBEB. And messages will be delivered to them like they are delivered to any other recipient. 

If your public folders are hosted in Exchange Online

Directory-Based Edge Blocking (DBEB) is not yet supported for Mail Enabled Public Folders hosted in Exchange Online.

But there are two possible workarounds:

1. Stop routing emails sent to Public folders to Exclaimer. No Server-Side signature will be applied. (Recommended)
   
   
2. Disable the Directory-Based Edge Blocking (Not Recommended)

To stop routing emails sent to Public folders to Exclaimer (Recommended):

1. Log into Exchange Online.
   
   
2. Navigate to Mail flow, then select rules.
   
   
3. Select the rule Identify Messages to send to Exclaimer.
   
   
4. Click Edit.
   
   
5. Scroll down to the Except if... section.
   
   
6. Click on add exception.
   
   
7. Select the Recipient... Is this person.
   
   
8. In the Select Member's dialog, select all of the public folder mailboxes.
   
   
9. Click Add.
   
   
10. Click OK, then click Save. 

To disable Directory Based Edge Blocking (Not Recommended)

1.  Log into Exchange Online.
   
   
2. Navigate to Mail flow, then select Accepted domains.
   
   
3. Select the domain of the public folder, then click Edit.
   
   
4. Under This accepted domain is select Internal relay to disable DBEB.
   
   
5. Click Save.