You can be notified by email whenever you have a new subsciber to a List, and if you wish you can have that notification sent to as many other email addresses as you need, as below, just seperate them with a comma and one space.
In Lists > Your List > Edit List
The notification email will be sent from your campaign “from” email address.
NOTE: It is not practical to make this function available when Subscribers are added via the SendReach API as one can import Lists via the API, and obviously one can not make it possible for an Alert Email to be sent as a result of a List of 50,000 subscribers being imported!
When integration is achieved using HTML Form Code the New Subscriber Notification Email is triggered as a List cannot be imported that way.