Hotmail mail admin

[fiberOptiC]

I'm looking for a hotmail mail admin or someone with the information I'm
looking for.
I have a client that is trying to block the world, but only allow certain ip
addresses through.  It looks like hotmail uses a large pool of ip addresses
for attachments so we've had a hard time determining what ip addresses to
allow. My client specifically is requesting this be allowed.  Does anyone
know what addresses hotmail users for their attachment servers or would a
hotmail admin be willing to contact me off list with this information?

Thanks!