The folks over at ClaimID have recently added a “contacts” feature to their site, which makes it one of the first sites to attempt a decentralized social networking feature. They ran into a problem in that when adding an arbitrary OpenID identifier to your contact list, there is no obvious way to contact them and get them to verify the relationship. ClaimID's current solution is to have users enter both an OpenID identifier and an email address, which works after a fashion but is a little redundant.
It is with this use-case in mind that I've drafted up the “Send a Message” Protocol, which is a very simple protocol built on top of OpenID Exchange that allows a site to send a message on behalf of a user to an OpenID Identifier — assuming that the recipient actually supports this protocol, naturally.( Collapse )