code: func validateNotification(c *validation.Context, cfgNotification *notifypb.Notification) {
  	if cfgNotification.Email != nil {
  		for _, addr := range cfgNotification.Email.Recipients {
  			if _, err := mail.ParseAddress(addr); err != nil {
  				c.Errorf(badEmailError, addr)
  			}
  		}
  	}
  }
docs: // validateNotification is a helper function for validateConfig which validates
  // an individual notification configuration.