discourse/lib/email.rb

require 'mail'
module Email

  def self.is_valid?(email)

    parser = Mail::RFC2822Parser.new
    parser.root = :addr_spec
    result = parser.parse(email)

    # Don't allow for a TLD by itself list (sam@localhost)
    # The Grammar is: (local_part "@" domain) / local_part ... need to discard latter
    result && result.respond_to?(:domain) && result.domain.dot_atom_text.elements.size > 1
  end

end