Ebay does not allow email and certain other details to be shared in messages as they do not want the transaction taken out of their ecosystem. This is partly a protection mechanism for you, as well as making sure the seller does not avoid fees.

You would definitely compromise your own account if you shared those details with the seller.

You might want to phone up Customs and find out what duties are possibly going to be owing (assuming it arrives). Ebay now collect GST as part of the transaction, and you would see this on your invoice, but not sure if there might be further fees to pay.