The guy who wrote the article is in South Africa. It wouldn't be surprising that big parts of the world are grey or blacklisted for e-mail. But note that having

The guy who wrote the article is in South Africa. It wouldn't be surprising that big parts of the world are grey or blacklisted for e-mail. But note that having an e-mail server in the US often negates the benefit of maintaining an own e-mail server for anybody not in the US.