Techniques are described herein for a messaging system to allow publishers that are aware of the identities of their respective subscribers to target content at those subscribers directly. This may be accomplished by allowing users and other targets (e.g., groups) to register their identities at particular computing nodes of a system. Then publishers (e.g., applications) may send out messages targeted at particular identities, and a publishing system may forward messages to appropriate nodes based on which identities are registered at those nodes. Legacy applications that are not able to target particular identities may instead connect to application adapters that are configured to learn which identities should be targeted by each application. In addition, anonymized identities may be used for application messages that need to cross between domains having differing security levels.