I know this, it isn't about being an open relay, it's more that the users (and/or suspicious software on their computers) sometimes do weird things, like send mail from
username@hotmail.com to
target@xs4all.nl through the Scalix system. They shouldn't be able to, I don't want them doing stuff like this, since it sometimes causes mail to loop (not Scalix' fault, other elements of our setup are causing this, but Scalix simply discarding mail not either to or from it's own domain should fix the problem, it's not the only solution, but the only one that doesn't involve me rewriting a Perl script I don't quite understand (don't speak perl) and thus the one I would prefer).