TheSecond.Email is an email that is online when you are online.
As a user, I want to receive email only when I'm online.
What if we can provide an email address to the user that is active ONLY when the user is online and expecting an email?
When the user is online (ie., logged into the webpage offering this service), the email is delivered to their inbox, ie., the web page they are on.
When the user is offline, the email is rejected, possibly with a 450.