mail problem

[gm]

Hey guys,

I found out that my server (FC1) has been blacklisted by some sites. I
was wondering if there's a way to determine why it's been blacklist. I
think it's because there mite be an open relay in my server. I was
wondering if there's a way to test for this on my server? In general I
was wondering how to test the security of my network on the whole in
case there are other leaks on the network.

Cheers

GM