Message Audit Log Details shows that delivery has failed. The delivery details show a message in the format:

### #.#.# Response message

550 5.7.1 message rejected due to content restrictions

The Delivery Details show a response from the destination mail server rejecting the message due to some policy or content filtering. 

• You will need to review the SMTP transactions and/or diagnostic log files from the receiving MTA referenced in the "Attempted Delivery to:" of the Message Audit Log.
• This message is a delivery response from another MTA that Messaging Gateway is reporting, not a message that is being generated by the Messaging Gateway itself.