single_recipient_smtp.rb

module SingleRecipientSmtp
  def self.included(clazz)
    clazz.class_eval do
      cattr_accessor :single_recipient_smtp_settings
    end
  end

  def perform_delivery_single_recipient_smtp(mail)
    mail.to = single_recipient_smtp_settings[:to]
    mail.cc = nil
    mail.bcc = nil
    perform_delivery_smtp mail
  end
end

staging.rb

config.action_mailer.delivery_method = :single_recipient_smtp
ActionMailer::Base.send :include, SingleRecipientSmtp
ActionMailer::Base.single_recipient_smtp_settings = {
  :to => 'staging@example.com'
}