Other Function.
・Special rule for the combination of Sender(Or Sending Domain) and Recipient (Or receive domain)
・Selectable password option. One time password, Fixed password, Password mail back to sender, etc.
・Switching Encrypt/Not Encrypt by mail subject keyword.
・For compliance function, Prohibit extension, Prohibit recipient, etc.
・Customizable message template.
・It takes 50 years to hack 8 digit password by brutal attack. (2008 IT research by Japan Research Organization.)