22. A method comprising: receiving first activity information for a sender of a first link to at least one recipient collected by a collection resource at a Web site; storing the first activity information at a storage server; receiving second activity information when a recipient accesses the first link sent by the sender corresponding to the first activity information stored at the storage server, wherein a personally identifiable information of the recipient includes an e-mail address of the recipient, and no personally identifiable information of the recipient collected in collecting the second activity information; using at least one processor, attempting to identify a first node representative of the sender in a social graph; when a first node representative of the sender in a social graph is not identified and after receiving the second activity information, creating a second node to represent the sender in the social graph; and based on at least information associated with the second node in the social graph, selecting a personalized digital content for delivery to at least one of the recipient or sender.
23. The method of claim 22 wherein the selecting a personalized digital content for delivery is in response to at least one of a bid request from a real-time bidding exchange or an ad request from a publisher network.