A digital postal mail delivery service provides a mail push notification service (MPNS) whereby recipients of sender mailers are invited to join the service in a secure and seamless manner. Preferably, MPNS notifications are provided periodically, continuously, or on demand, and these notifications may be coordinated with other physical or digital mail activities to increase the likelihood of converting new users to the service. The MPNS service takes advantage of publicly-accessible sources of user information to build a registry of potential users who can be matched to information provided by the senders. Upon receipt of a push notification, a customer may register for the service; during that registration, the service verifies the customer's identity and residence in a secure and efficient manner, preferably using the information originally obtained from the sender.