Returning Mailbox Unavailable status "Online"

[Doron <pe...@hotpop.com>]

Hi there,

I have a matcher for a specific group of users and a 1 mailet to handle
messages for these users.
For all other users I would like James to return the status "550 Mailbox
Unavailable".
Namely, when another SMTP connects to my James server, right after the line:
rcpt to:<ba...@my.domain>
The required outcome is - James returns "550 Mailbox Unavailable"
(assuming that bad_user doesn't comply with the matcher).

It looks quite simple, yet I haven't found any documentation about it.
I did come up with a (quite poor) workaround - having the
"local-address-error" processor
handle these messages. This will return *a reply* to the original message in
this format:
"We were unable to deliver the attached message because of an error in the
mail server. Error message below: 550 - Requested action not taken..."

What I really need is an undeliverable message (like you'll get after
sending a mail do unknownMailbox765@hotmail.com)

Thanks for your help,
- Doron