You could simply set up a fairly "generic" product without any optional settings enabled, to take orders and build a Buyer List for your webinar product. Then you could use our Newsletters feature to send everyone on that list a notification with your instructions to access each webinar session:
This would be most reliable if you only use PayPal Standard to handle your E-junkie checkouts, since buyers will automatically be opted-in to join your list. Other checkout methods would present a checkbox the buyer would need to deliberately tick in order to opt in, so you'd need to remind them of that if you want to accept non-PayPal payments.
For more full-featured mailing-list services, you could use Aweber to manage subscriptions and send messages, and use our Aweber integration method to have the product automatically submit each buyer's name/email to your Aweber list:
Note that, aside from the opt-in caveats described above, Aweber would also send each new subscriber a confirmation email with a link they must click to confirm their desire to join the webinar list.
You could also just use our generic custom/3rd-party Integration method to send all order data to the URL of a script you'd maintain on your server, and this would not depend on any opt-ins beyond actually buying the product, but you'd be more responsible for receiving that data and doing whatever you require with it: