Neat tip. Keep in mind that with all the modern email server "cloaking" and anti-spam measures this is not an absolute test. If the server rejects it, you can

Neat tip. Keep in mind that with all the modern email server "cloaking" and anti-spam measures this is not an absolute test. If the server rejects it, you can be fairly sure the address is invalid. If it accepts it, you cannot 100% sure that an email actually sent to that address would get delivered all the way through to a physical mbox.