Enviar correo electrónico al administrador por registro de nuevo usuario

[merefield (Robert)]

Con gusto lo revisaría por ti, pero ¿no resuelve esto tu problema?:

Email notification for "must approve users"

The frequency of the reminder is controlled by the pending users reminder delay site setting. The default value of that setting is 8 hours. Try setting it to a lower value. The pending user notifications are triggered by a background job that is run once per hour. This means that setting the pending users reminder delay to 0 will still cause the notifications to only be generated once per hour. Note that these notifications are only sent to site moderators, not to site admins.