Rails.application.configure do
  config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.perform_deliveries = true

  # more codes

end

development:
  SENDGRID_USERNAME: something@heroku.com
  SENDGRID_PASSWORD: something

ActionMailer::Base.smtp_settings = {
  address: 'smtp.sendgrid.net',
  port: '587',
  authentication: :plain,
  user_name: ENV['SENDGRID_USERNAME'],
  password: ENV['SENDGRID_PASSWORD'],
  domain: 'heroku.com',
  enable_starttls_auto: true
}