Live account is different for authorize.net , they have two mode there (Test,Live). On test mode error was not showing but on live mode "Email is required" error showing. Sandbox account was different.
I am using credit card payment by authorize.net plugin and showing error message that "Email is required". We unchecked required field from Authorize.net site as well. It was working on sandbox as well as on test mode. When i changed the mode to "Live" from authorize.net then it was showing this error. I am using nopcommerce 3.7 version.