[exim] relaying woes

Hi all,

I've spent the past weekend setting up this network with two machines.
nexus and mx1.

nexus is a webserver, and mx1 is a mailserver. i set up exim on nexus to
use mx1 as its smarthost, which i presume means it'll use it as an smtp
gateway.

unfortunately, both machines keep logging stuff like:

2005-09-19 13:49:15 refused relay (host) to <oren.mazor@???> from <>
H=nexus.carleton.ca (nexus) [134.117.76.10]

i went thru the config a few times, edited the config files, farked with
nexus, and frankly, I've no idea what else to check. all of my googling is
turning up spam and anti-spam related discussions for this type of error.

any help would be greately appreciated!

thanks
Oren