module Devise::Mailers::Helpers

def mailer_sender(mapping, sender = :from)
  default_sender = default_params[sender]
  if default_sender.present?
    default_sender.respond_to?(:to_proc) ? instance_eval(&default_sender) : default_sender
  elsif Devise.mailer_sender.is_a?(Proc)
    Devise.mailer_sender.call(mapping.name)
  else
    Devise.mailer_sender
  end
end