How to configure DSN for Apache James SMTP Server

[Adam Raszkiewicz]

I'm looking to set DSN message for unknown/non-existing user on Apache James 
SMTP server.
Now it rejects a message to that kind of user on the FastFail module but for 
that I can't find any information how to set DSN message with valid 
Content-Type, DSN Action and DSN Status instead sending an empty default one.
mailetcontainer.conf for DSNBounce looks like:

<processor state="bounces" enableJmx="true">
  <mailet match="All" class="DSNBounce">
    <passThrough>false</passThrough>
    <attachment>message</attachment>
    <messageString>Here is [machine]. I'm not able to deliver this 
message.</messageString>
  </mailet>
</processor>

Thanks,
Adam