Rails Email Setup for Development, Staging, and Production

action_mailer.rb

# config/initializers/action_mailer.rb 
Rails.application.config_for(:mailer).keys.each do |option_name|
  Rails.configuration.action_mailer[option_name] = Rails.application.config_for(:mailer)[option_name]
end

mail.rake

# lib/tasks/mail.rake
namespace :mail do
  desc "Send a couple of test emails"
  task send_tests: :environment do
    %w[ a@example.com b@example.com ].each do |recipient|
      puts "Mailing #{recipient}..."
      TestMailer.with(recipient: recipient).test_mail.deliver_later
    rescue => exception
      log_data = { task: "mail:send_tests", recipient: recipient, exception: exception }
      Rails.logger.error(log_data)
    end
  end
end

mailer.yml

# config/mailer.yml 
development:
  asset_host: "http://www.railsgigs.test:3000"
  default_url_options:
    host: "www.railsgigs.test"
    port: 3000
  smtp_settings:
    address: "localhost"
    port: 1025

production:
  asset_host: <%= "https://#{ENV["URL_HOST"]}" %>
  default_url_options:
    host: <%= ENV["URL_HOST"] %>
  smtp_settings:
    user_name: <%= ENV["SMTP_USER_NAME"] %>
    password: <%= ENV["SMTP_PASSWORD"] %>
    domain: <%= ENV["SMTP_DOMAIN"] %>
    address: <%= ENV["SMTP_ADDRESS"] %>
    port: <%= ENV["SMTP_PORT"] %>
    authentication: <%= ENV["SMTP_AUTHENTICATION"]&.to_sym %>
    enable_starttls_auto: true

test:
  default_url_options:
   host: "www.railsgigs.test"
   port: 3000

Hi!

I was just adding your config into a Rails 5.2 app and ran into an issue with the initializer, because back in those days the result from config_for was a hash with String keys rather than symbols. As a result the SMTP settings don't get picked up correctly by ActionMailer. Here's an initializer that works on 5.2:

Rails
  .application
  .config_for(:mailer)
  .deep_symbolize_keys
  .each { |key, value| Rails.configuration.action_mailer[key] = value }