rails 3:如何在动作邮件中中止交付方式？

class UserMailer< ActionMailer::Base
  def welcome_email(user)
    @user = user
    @url = "https://example.com/login"
    mail(to: @user.email, subject: "Welcome to Example.com")
    return if @user.email.include?("example.com")
  end
end