ActionView::Template::Error: Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true

Question

My ruby on rails action mailer runs all good in development environment, but in production environment, it keeps throw:

ActionView::Template::Error: Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true

My development config is

config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  :port           => xxx,
  :address        => 'smtp.example.org',
  :user_name      => '[email protected]',
  :password       => 'xxxxxxxx',
  :domain         => 'xxxxxx.com',
  :authentication => :plain,
}

config.action_mailer.default_url_options = { :host => 'localhost:3000' }

My production config is

config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  :port           => 587,
  :address        => 'smtp.example.org',
  :user_name      => '[email protected]',
  :password       => 'xxxxxx',
  :domain         => 'example.com',
  :authentication => :plain,
}
config.action_mailer.default_url_options = { :host => 'example.com' }

My other environments are:

ruby 2.1.1
rails 4.0.3
sidekiq 
devise
devise-async

I have tried:

1. Add the following in a initializer file

   ActionMailer::Base.default_url_options[:host] = "example.com"
   

2. This answer here

Neither of them works.

Answer 1

In the end I added the following with the correct value to each environment file:

test.rb / development.rb / production.rb

Devise 3.2.x - 4.x.x

Rails 4.1.x && Rails 4.2.x && Rails 5.x.x

Thanks to maudulus

# Default Mailer Host
  Rails.application.routes.default_url_options[:host] = 'domain.com'