Okay, that could be a workaround for me, though I’m sure some people won’t manage to add their email-address to the url. What happens if you use the url without an email address?
Wouldn’t it make sense to allow users to enter their email on the invitation page just like they can add/modify the username (assuming it works the same way as with ordinary invite links)? If people can modify the email in the url, there isn’t really any reason to make it a required field, is there?