Check common mailbox and user names

When you let users of a webapp create their own usernames, and this name is used in an email address or Unix user, it is important to check against some common usernames, like 'root', 'postmaster', and 'postfix'. This library is an attempt for that.

You should check the following:

• The address in your WHOIS, wich may be used for things like registering a
  TLS certificate. It should really be something like hostmaster@ anyway, so
  this should not be an issue.
• If you make Unix accounts with these names, check which names occur in
  /etc/passwd (and possibly /etc/group).

License: BSD 2-clause

Resources:

• RFC2142_
• Security StackExchange: What email addresses are treated as trusted_
• Postbit reserved username list_
• /etc/passwd and /etc/group on my laptop (Debian testing/stretch).
• shouldbee's list_
• kwappa's list_

.. image:: https://imgs.xkcd.com/comics/exploits_of_a_mom.png

Image via xkcd.com_

.. _RFC2142: https://www.ietf.org/rfc/rfc2142.txt .. _Security StackExchange: What email addresses are treated as trusted: http://security.stackexchange.com/questions/84127/what-email-addresses-are-treated-as-trusted .. _Postbit reserved username list: http://blog.postbit.com/reserved-username-list.html .. _shouldbee's list: https://github.com/shouldbee/reserved-usernames .. _kwappa's list: https://github.com/kwappa/username_not_reserved_validator/blob/master/lib/username_not_reserved_validator/reserved_names.rb .. _xkcd.com: https://xkcd.com/327/