Currently though my Telecom customers though are unable to send directly to microsoft mail services (hotmail.com/outlook.com/msc.co.nz/etc etc as Microsoft have blocked an entire Telecom IP block but not smtp.xtra.co.nz. For these clients I do redirect any hotmail/outlook/msn email to a send connector using smtp.xtra.co.nz.

Interesting you mention that. I have decided I cannot be bothered troubleshooting individual exchange servers anymore, so I just route our customers through our hosted service as a smarthost and deal with it centrally. Then when they upgrade from SBS2003 or exchange, we are now moving them entirely onto the hosted platform. That way I have one server to troubleshoot and its super easy since its in my own ip space :-)

Do you mind telling us what hosted service you use for this?
I'm trying to find something for our customers.