But nothing is stopping the user from supplying a proxy email address in your textbox where you ask for a non-proxy email address. Sending a test email doesn't tell you whether the user-supplied email address is a proxy email address or a non-proxy email address, since your test email will go through in either case. That's the whole point of a proxy email address instead of a completely fake email address, is that emails sent to the proxy email address will still go through.
