Sent a "User unknow" on a relay server ?

[Noc Phibee <noc@phibee.net>]

Hi

i have a Smtp In relay server on Qmail, on this server, he don't have
account. He receive the email and after sent to the good server based on
smtproutes.

For one domain, i want that this relay sent a "User Unknow" when the to:
are not into
a file list (or MySql). It's possible ?

For sample:

i have a file:

name1@domain.com
name2@domain.com
name3@domain.com

if a user sent to name2@domain.com => Ok that' relay
if he sent to aaaa@domain.com => not into the File reject "User Unknow"

It's for only one domaine, all other domain are in *@other-domain

Thanks for your help