The following functionality allows you to receive email notifications for subscription events.

While on your store admin's Manage Product Categories, enable send admin email in the Email Options, input the email addresses you want to be notified in admin email(s), and then set an admin email subject.

At this snippet in the admin text email template if you want to be notified whenever a customer registers a new subscription.

{% set is_new_sub = 0 %}
 
{% if has_subscriptions %}
{% for subscription in subscriptions %}
	{% if subscription.original_transaction_id == transaction_id %}
		{% set is_new_sub = 1 %}
	{% endif %}
{% endfor %}
{% endif %}
 
{% for item in items %}
	{% if item.name == "Past Due Amount" %}
		{% set is_new_sub = 0 %}
	{% endif %}
{% endfor %}
 
{# WRITE EMAIL BODY BELOW #}

In case you want to modify the email subject to be more descriptive to the newly-created subscription event, add this snippet below:

{% if is_new_sub and not is_subscription_cancel and not is_subscription_modification and not is_updateinfo %}
{% set custom_subject = 'New Subscription by ' ~ billing_address.first_name ~ ' ' ~ billing_address.last_name ~ ' [' ~ order_id ~ ']' %}
{{ custom_subject|fc_output_data('email_subject') }}
{% endif %}

At this snippet in the admin text email template if you want to be notified whenever a customer cancels a subscription.

{% if is_subscription_cancel %}
{# INSERT CUSTOM CODE HERE #}
{% endif %}

As with the above optional snippet, you can include this in the custom code section of the cancelled subscription condition:

{% set custom_subject = 'Cancelled Subscription by ' ~ billing_address.first_name ~ ' ' ~ billing_address.last_name ~ ' [' ~ order_id ~ ']' %}
{{ custom_subject|fc_output_data('email_subject') }}

At this snippet in the admin text email template if you want to be notified whenever a customer modifies a subscription.

{% if is_subscription_modification %}
{# INSERT CUSTOM CODE HERE #}
{% endif %}

You could also change the email subject as you would with the newly-added and cancelled.

Feel free to combine the conditions in one conditional statement separated by an and statement.