How to confirm a Google user’s specific email address
Is this really even a big issue? For one, you have to already have knowledge of the email address in advance. Then you have to somehow get this user to go to a page that you have control over. Then you have to get them to wait around on your page while you run through 1000 possible email addresses every 25 seconds. Unless this got onto a really, really compelling page, I don't think anyone is going to sit around waiting for a page like this to do its business. The chances of getting a successful match are so low that I can understand why it's not a priority to fix this.