Redmine

I switched my mail settings from

default:
  delivery_method: :smtp
  smtp_settings:
     address: "smtp.my-server.com" 
     port: 25

to

default:
  delivery_method: :async_smtp
  async_smtp_settings:
     address: "smtp.my-server.com" 
     port: 25

for performance reasons.

With async_smtp I get the following error (in production.log), if I try to save I new ticket or if I edit an existing ticket:

ActiveRecord::StatementInvalid (Errno::ECONNREFUSED: Connection refused - connect(2): UPDATE `custom_values` SET `value` = '0' WHERE `custom_values`.`id` = 5011):
  config/initializers/10-patches.rb:137:in `block in deliver!'

There are no problems with smtp (without async).

Redmine version                2.5.3.stable
  Ruby version                   2.0.0-p576 (2014-09-19) [x86_64-linux]
  Rails version                  3.2.19
  Environment                    production
  Database adapter               Mysql2