Redmine

Here is my configuration.yml about mail settings:

production:
   email_delivery:
     delivery_method: :async_smtp
     #delivery_method: :smtp
     smtp_settings:
       #tls: true
       enable_starttls_auto: true
       address: "smtp.gmail.com" 
       port: 587
       domain: "test.com" # 'your.domain.com' for GoogleApps
       authentication: :plain
       user_name: "admin@test.com" 
       password: "test" 

When the delivery_method change to :smtp, everything works fine. But when using async_smtp, it returns:

>rake redmine:email:test[test] RAILS_ENV=production
  Setting Load (1.5ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'sequential_project_identifiers' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'default_projects_public' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'default_projects_modules' LIMIT 1
  Tracker Load (0.1ms)  SELECT `trackers`.* FROM `trackers` ORDER BY trackers.position ASC
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'plugin_redmine_git_hosting' LIMIT 1
  User Load (0.1ms)  SELECT `users`.* FROM `users` WHERE `users`.`type` IN ('User', 'AnonymousUser') AND `users`.`login` = 'test'
  Setting Load (0.2ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'default_language' LIMIT 1
  Setting Load (0.2ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'host_name' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'protocol' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'app_title' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'mail_from' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'bcc_recipients' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'emails_header' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'emails_footer' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'plain_text_mail' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'text_formatting' LIMIT 1
  Setting Load (0.1ms)  SELECT `settings`.* FROM `settings` WHERE `settings`.`name` = 'cache_formatted_text' LIMIT 1
An error occurred while sending mail (Connection refused - connect(2))