[exim] redirect :fail: message in message/delivery-status

When I use a ":fail: some descriptive message" result in a redirect
router, the NDR generated has in the message/delivery-status part:

---------------
Reporting-MTA: dns; myself.example.net

Action: failed
Final-Recipient: rfc822;test@???
Status: 5.0.0
---------------
(names have been changed to hide the guilty)

compared to a normal bounce
Remote-MTA: and Diagnostic-Code: are both missing

Is there any way to get some descriptive message in there too, or do
i need to use a different method like, say, the autoreply transport?

Should I look at patching the source?


Jasen.
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