Scalix Reject unknown users at SMTP protocol level
This issue is almost not worth documenting, but it took me a while to figure this out:
http://www.scalix.com/forums/viewtopic.php?t=11741&highlight=
The short trick is to properly configure /etc/mail/local-host-names with the actual hostnames of the server, e.g.:
# local-host-names - include all aliases for your machine here. youdomain.com mail.yourdomain.com tux.yourdomain.com