ON THIS LINK

How someone could enter the wrong email address into one of these forms is beyond me.

the quick answer is gmail. The uniformity of an interface makes it prone to mistake by maximizing the likehood of the mistake. If everyone has a different domain lucia@example.org and lucis@example.net have more chances to be detected as mistakes by the server. but if everyone is using a unique email service with millions of users, all the possible names are indeed likely. Then when someone makes a typo the mail indeed arrives somewhere instead of generating a “Sorry, No User Here”.