[enonevets]

I don’t think this would work for users using aliases for their email signups.

In the existing system, [e-mail] can be verified.

In the proposed reverse method, sending emails from [e-mail], not [e-mail], breaks the sign up flow.

This is true for catchall emails where people register using [e-mail] (a forwarding address) but their real address, [e-mail], as well.

[woodruffw]

You're right. I'd actually argue (maybe controversially) that this is a feature -- tags and other optional metadata in email addresses are not standardized as unique identities; they're just how Google and a few other email providers have decided to interpret the local part.

That being said, I make use of Google's +-style filtering, so this would also break my own uses :-)