Rails Tutorial case sensitive not working
email_regex = /A[w+-.]+@[csupomonad-.]+[edu]+z/i

     validates :email, :presence   => true,
                        :format     => { :with => email_regex },
                        :uniqueness => { :case_sensitive => false }

def create
      user = User.authenticate(params[:session][:email],
                             params[:session][:password])
    if user.nil?
      flash.now[:error] = "Invalid email/password combination."
      @title = "Sign in"
      render 'new'
    else
      sign_in user
      redirect_to root_path
    end
  end

class User

  # all email writes get lowercased
  def email=(value)
    self[:email] = value && value.downcase
  end

end

user = User.authenticate(params[:session][:email].try(:downcase), ...)

validates :email, :presence   => true,
                  :format     => { :with => email_regex },
                  :uniqueness => { :case_sensitive => false }