Differentiating Message Deliveries

The simple SIRP model not only puts more burden on spammers but also regular contacts of a receiver. To address this issue a hybrid email delivery system can be designed to support both the sender-push and receiver-pull models. In such a system, each receiver maintains a list of regular contacts, whose complete messages can be directly pushed from the senders to the receiver using the current SMTP protocol. In addition, a list of blacklisted contacts can be summarily declined. Messages from non-regular contacts should be stored and managed by the sender mail servers, and only the envelopes of such messages are directly delivered to the receiver to notify the pending messages.