I'm new please be nice 🙂

Even though an item that I listed, said that I only ship to Australia, someone used *buy it now* from the USA.  I don't trust the source, he/she wants me to contact them outside of ebay mailing. I've just contacted them through ebay question, and invoiced them.  My questions are, how do I stop being from overseas bidding on my item?  and do buyers have access to my email address outside of ebay.

Thanks a lot 🙂