* Recurring Payments Demo
* How Recurring Payments Work
* Recurring Payments Terms
* Recurring Payments With Express Checkout
* Options for Creating a Recurring Payments Profile
* Recurring Payments Profile Status
* Getting Recurring Payments Profile Information
* Modifying a Recurring Payments Profile
* Billing the Outstanding Amount of a Profile
* Recurring Payments Notifications

Source from paypal

Additional source: http://articles.techrepublic.com.com/5100-10878_11-5331883.html

For Recurring Payments Notifications, you can use IPN. Merchants are notified of certain events through IPN. For recurring payments profiles created using Express Checkout, buyers are also notified of specific events by email.

To activate the IPN, you need to login to your account and activate it from “Instant Payment Notification Preferences” Menu.

Once payment, subscription started, or subscription ended it will execute the url you entered in IPN setting.

Here are the request from paypal for recurring payment:

Pay

transaction_subject:, payment_date:00:24:20 Jan 29, 2010 PST, txn_type:subscr_payment, subscr_id:I-TR8AEDTYY3A3, last_name:,,
residence_country:ID, payment_gross:0.10, mc_currency:USD, business:myemail@domain.com, payment_type:instant,
protection_eligibility:Ineligible, verify_sign:AwVFRrppcBWp.SbFNfxVhWwgMJq1AzhZhdCLslBXMKqUWPTs7OhhthbB,
payer_status:verified, payer_email:client@domain.com, txn_id:9E184006CH967554N, receiver_email:myemail@domain.com,
first_name:Adri, payer_id:BRF4CDPWN84AC, receiver_id:DVFZ59JCMFVEN,payment_status:Completed,payment_fee:0.10, mc_fee:0.10, mc_gross:0.10, charset:windows-1252, notify_version:2.9,

subscribe

txn_type:subscr_signup, subscr_id:I-TR8AEDTYY3A3, last_name:,, residence_country:ID, mc_currency:USD,
business:myemail@domain.com, amount3:0.10, recurring:1, verify_sign:A8s9ZB.gPMzpWoypvEK3Oi8kH04SA6rxIBluaeZfMSHesjkeOATMaJRe,
payer_status:verified, payer_email:client@domain.com, first_name:Adri, receiver_email:myemail@domain.com, payer_id:BRF4CDPWN84AC, reattempt:1, subscr_date:00:24:19 Jan 29, 2010 PST, charset:windows-1252, notify_version:2.9, period3:1 M, mc_amount3:0.10,

cancel

txn_type:subscr_cancel, subscr_id:I-TR8AEDTYY3A3, last_name:,, residence_country:ID, mc_currency:USD, business:myemail@domain.com, amount3:0.10, recurring:1, verify_sign:AwLeRoV0CcJ4bqIPyyj4pN2QzIoEA1eWFEwodSF46c0b-.d2eIQHFjiE,
payer_status:verified, payer_email:client@domain.com, first_name:Adri, receiver_email:myemail@domain.com,
payer_id:BRF4CDPWN84AC, reattempt:1, subscr_date:00:24:19 Jan 29, 2010 PST, charset:windows-1252, notify_version:2.9, period3:1 M, mc_amount3:0.10,

There are two variable you need to check txn_type and subscr_id.

You can see that txn_type can be subscr_payment, subscr_signup, and subscr_cancel