The idea here is applicable to end to end encrypted messaging in general. Basically the identity information for a user specifies more than one encryption key in a secure way. Someone sending a message to that user then knows that the user wants the message encrypted for all the given encryption keys.<p>The idea here is to make end to end encryption more acceptable to companies with compliance or legal obligations to archive messages. It is generally applicable to any situation where the employee is unavailable to decrypt their messages where that is a problem.<p>The second encryption key of an employee would be the archive identity. The archive identity would be controlled by a trusted person or persons who would only have to dig into the archive if there was an actual issue. Otherwise the archive could be left secure.