Since the last few weeks we are experiencing a problem with sending out an external note communication.

When sending out extern note communication. We get the following error message:

„Sending of this message has failed. [25/03/2024 15:13 (Europe/Brussels)] Could not send message to server: 550, 5.7.64 TenantAttribution; Relay Access Denied [No TLS] [DB1PEPF00050A00.eurprd03.prod.outlook.com 2024-03-25T14:13:12.919Z 08DC491644ECAF68] !“

We have made 0 changes in the Otobo as well as our Exchange server side. Email communication seems to be working as normal.

Any idea where we can start with the investigation? The MX record in our exchange is correct configured.