Validation email

HI

I recently booked an appointment with our Microsoft Rep via bookings and prior to being able to make the booking, I was emailled a validation code that i had to enter prior to my booking being made.

I was really impresssed! As this solves the issue with no check on whether the email address was valid or not when making a booking.

Does anyone have any information on this facility or how it was achieved? This would be perfect when making our services available to the public to book.