If you're setting up a service where people can register their own usernames to be used as a hostname (username.example.com), email address (username@example.com), or URL path (example.com/username) within your domain, there are some common names you should avoid letting the general public register.

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This is a list of all the names I know that should be restricted from registration in automated systems. If you know of others, please let me know and I'll update this page.