Australia is part of the 5 eyes alliance which automatically shares data between the US/Canada/UK/New Zealand which means it is a safe bet that the US can get this data as easily as it would be on it's own soil.

As an American storing data in Australia creates another problem. The US can't spy in the US on it's own citizens but another country can at the request of the US government and will report everything back to the US.

I would pick Russia or China first...

Or just use protonmail which is designed to offer some protection.