Which email opens in all countries without security check?

Doesn't exist. There are checks being done by NSA, GCHQ and the great Chinese Firewall, just to name a few. Even if you build your own unchecked email system, you want to communicate with people outside ofo your system and at that moment, the content of the emails is vulnerable.

You can circumvent this by encrypting your emails, but that requires that the recipient has the other part of the software to decrypt it.

none of emails