production.rb

  config.action_mailer.default_url_options = { host: 'domain.com.br' }
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.perform_deliveries = true
  config.action_mailer.default charse: 'utf-8'

  config.action_mailer.smtp_settings = {
      :address   => "smtp.sendgrid.net",
      :port      => 587, # ports 587 and 2525 are also supported with STARTTLS
      :enable_starttls_auto => false, # detects and uses STARTTLS
      :user_name => "apikey",
      :password  => ENV["SENDGRID_API_KEY"], # SMTP password is any valid API key, when user_name is "apikey".
      :authentication => 'plain',
      :domain => 'domain.com.br', # your domain to identify your server when connecting
  }

Completed 500 Internal Server Error in 487ms 
ArgumentError (SMTP-AUTH requested but missing secret phrase):
 app/controllers/contacts_controller.rb:9:in `create'