application.rb

module Emailery
  class Application < Rails::Application
    config.action_mailer.delivery_method = :smtp
    config.action_mailer.smtp_settings = {
      address:              'smtp.mandrillapp.com',
      port:                 587,
      domain:               'example.com',
      user_name:            '[email protected]',
      password:             'ZNrasQmPJPybqX_gsihNdQ',
      authentication:       'plain',
      enable_starttls_auto: true  
      }
      
    config.active_record.raise_in_transactional_callbacks = true
  end
end

notifications_controller.rb

class NotificationsController < ApplicationController
  def show
  end

  def create
    NotificationsMailer.contact(email_params).deliver_now
    redirect_to :back, notice: "Your email was sent."
  end

  private

  def email_params
    params.permit(:name, :email, :message)
  end
end

notifications_mailer.rb

class NotificationsMailer < ApplicationMailer
  def contact(email_params)
    @message = email_params[:message]

    mail(
      to: email_params[:email],
      subject: "Mensaje de #{email_params[:name]}",
      )
  end
end