can it be that 4xx errors are not being reported back to the client?
From None@21:1/5 to All on Fri Apr 1 18:16:13 2022
When I reject messages with a 5xx code and error text, the sender is
most of the time being notified and given the error text.
It looks like the 4xx is not being relayed back to the sender (probably
because the server is instructed to try again later)
Is there an error response that informs the sender while the server
still keeps trying?