config code for email verification in config>>environment>>development.rb

.rb

 config.action_mailer.perform_deliveries = true
  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.default_url_options = { host: "localhost:3000" }
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
    user_name:      "username@gmail.com",
    password:       "password",
    domain:         "localhost:3000",
    address:       "smtp.gmail.com",
    port:          587,
    authentication: :plain,
    enable_starttls_auto: true
  }