I'm accepting this as the current answer. But might I suggest that this is probably not the best way to handle user creation/admin in general. While I understand the requirement for an email address to send notifications, it seems that even going with this line of thinking there should be no requirement for the email address to be unique, or user creation to be based on the idea of an "invitation" as opposed to the admin directly creating a user. If the requirement for email address uniqueness and the ability of an admin to directly create a user was added that would make for a much more sane, and more general purpose user system that would facilitate the creation of utility users for things like CI pipelines.
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