Rails 3.2 ruby 1.9.3 exception_notification in staging not able to send mail

I am applying exception notification gem for rails 3.2 application.

Following is my code

gemfile

gem 'exception_notification'

config/environments/staging.rb

Rails.application.config.middleware.use ExceptionNotification::Rack,  email: {
 email_prefix: '[Exception] ',
 sender_address: %('HPAE - Error' <mymail@gmail.com> ),
 exception_recipients: %w(mamail1@gmail.com)
}

It runs perfectly in my local but on server in staging its not working.

Thanks,