WDTBD, I'm usually sending to local major Australian servers (Telstra,Optus etc) as well as plenty of other hotmail accts.
Now that you mention it the problem could be with Telstra, any other Aussies care to comment on this.
BTW: Can you actually unsubscribe from that junk porn email that appears regularly? I've never bothered to open it to check, except maybe the "extend your @$#& by 3 inches" message. Now I'm interested...