Typically, when a message is bounced or blocked, the content of the message is returned to sender and to the local domain postmaster in the notification message. This can be a strain on resources if a number of very large messages are returned in their entirety. To block the return of content for messages over a certain size, set the CONTENT_RETURN_BLOCK_LIMIT option in the MTA options file.
The MTA fetches the block limit associated with the envelope return address and will set RET=HDRS if no return policy is specified and the message size exceeds the block limit. This prevents nondelivery reports for large messages from being undeliverable themselves. No new options or settings are associated with this change.