8010MSExchangeTransportRemoteDeliveryA message with the Internal Message ID 12345 was rejected by the remote server. This message will be deferred and retried because it was marked for retry if rejected. Other messages may also have encountered this error.
This message is logged when journaling is enabled (Organization - Hub Transport - Send Connectors), but the remote host receiving the journaling messages rejects the messages.
Review your configuration to ensure that journaling messages are sent to the correct host, contact the remote host administrator, or disable journaling.
Use the Exchange toolbox to view all messages in the journaling queue.